Plumbing

In the van there will be a small plumbing system. Since I don’t have a shower, and also don’t need an outdoor shower, its limited to the kitchen area only.

I also don’t have water tanks underneath the van, since I don’t need huge amounts of water. Also, I don’t think it’s hard to get water, so no need to take huge amounts with me.
So i went with 2 small portable water cans of 20 Liter each (5.3 gallon). If needed, I can fill a 3rd one and store it in the back.
Both of them can fit in one of the kitchen cabinets. One will be used for fresh water, the other one as grey water.

I use a small submersible pump, which is connected to the kitchen faucet. Inside the faucet is a small microswitch.
This switch is connected to a small relay, which switches the actual pump.
Some people are reporting issues with the small micro switch switching the inrush currents of a pump, so I added a relay, to save the microswitch.

I also installed a small 12V / 200W boiler. This can hold 6L water (1.6 gallon). I also added a switch so I can disable the boiler if needed to save some power. (I calculated the boiler to use approx 35Ah battery capacity, so it’s quite a heavy user…

The boiler is a plastic one, with rather crappy insulation. I’ve installed it below my bench. In order to add some insulation I’ve wrapped it in some 9mm Armaflex leftovers, made a small box around it, and filled that with sheep wool.
And it did fit perfectly, I had just enough to run the duct from the Webasto heater through this compartment as well.

Both the boiler and the water tanks are in separate compartments. I’ve covered both with Vinyl floor liner. Also made all sides fully watertight for at least 3cm (about 1 inch). On the back, there is a gap of 5cm widht (2 inches), so if anything starts leaking, it will leak into the structural framing of the van, which has holes in it so it will drop straight to the ground, instead of damaging my floor.

DIY LiFePO4 battery – Acquiring cells and hardware

So as in the previous post, I found the EVE 280Ah cells. People on https://diysolarforum.com/ have had very good experience with these, and also recommended some sellers on Alibaba to source these from.

So I went ahead and bought 4 cells for my build. The seller (Xuba) was able to provide me with DDP shipping (Delivery Duty Payed), so including all taxes and so on. Recommended by users of the forum was to use either boat or train as transport, since that would be much cheaper than shipping by air. Yes, it will be slower (Generally people mention 30-45 days) but that was fine for me.

In order to protect the batteries and monitor them, you need a BMS (Battery Management System). They are available in a whole bunch of options. Most of the DIY people tend to use Daly, Chargery, ANTBMS, or JBD. Some of them are sold under various other brand names, but they are the same.
I opted for the LTT Power (JBD) branded 4S LiFePO4 BMS :https://www.lithiumbatterypcb.com/product/4s-or-3s-12v-li-ion-or-lifepo4-battery-smart-bms-with-bluetooth-function-uart-and-rs485-communication-with-60a-to-120a-constant-current/

This BMS is fully adjustable, does have bluetooth and is affordable. It also can handle up to 120A, so a smaller inverter can be connected to the BMS. (In theory: any inverter <1400W, but I tent to not use a BMS above 50-60% of its rated current). So for a <800W inverter: No problem. Since my inverter is 1500W, I’ll use my inverter directly connected, only controlled by the BMS (more on that later)

The BMS
– Balances the cells so they remain equally in charge
– Protecs the cells for overcharge, and overdischarge

The Daly BMS is a good option, and is easier to install (1 complete unit, unlike a more PCB-like BMS as the one I have), but its very limited. With the LTT BMS I can adjust various settings more specific. Also, it has low-temp protection, where the Daly doesn’t have it.
(LiFePO4 cells can’t be charged below 0°C / 32F)
There is a new Daly Smart BMS on the market, but there aren’t many reviews yet, and its more expensive, so I did go for the LTT BMS.

So total costs are $320 (cells), $200 (Shipping) and $60 for the BMS, = $580 for 280Ah Lithium… Much more affordable than $1000+ for only 100Ah!

Battery upgrade to DIY LiFePO4 – Introduction and charger

As mentioned before, the lead acid battery of 105Ah and the Xenteq 10A charger are for testing and initial setup only. I was planning on upgrading to Lithium.

During the build, I found there are plenty of options for Lithium. You can get a complete battery, eg a Victron, Liontron, Battleborn, NDS, Wattstunde and a whole bunch of other sellers. Also, there are unknown / lesser known brands, slighly cheaper.
But in all cases: Still pretty expensive, a 100Ah battery easily is around 900 EUR in Europe

I did some calculations, and based on my requirements (beeing able to run offgrid for approx 2 days) I’ve calculated I needed at least 70-80Ah of usable capacity. So with lead-acid, this would mean around 180Ah, since lead acid can’t be discharged <50% without seriously shorten its lifetime.

If I want to run my water heater also, I estimated I need another 35-40Ah / day.
Using the inverter also adds up pretty much, so with 100Ah Lithium I can safely run my refrigerator, lights, fan, but usage of other equipment has to be done carefully and depending on the solar.

So: The bigger: the better. Off course, the drawback is the costs. With 200Ah of usable capacity it would be great, and basicly nothing to be worried about anymore (since the solar will also help, the 315Wp will charge the batteries even in shadown, although very limited. 200Ah = 400Ah lead-acid = way too much weight, so lithium is definitely the way to go.

Also, it would be pretty massive in size. After searching for options, I found there are a bunch of Chinese sellers selling very affordable batteries. Most popular are (as of aug 2020) the EVE 280Ah cells. (There are also 105ah cells available).

These are not Lithium-ion, but are LiFePO4. This is much more suitable for van usage: Safer to use/build and a lot easier: Each cell is 3.2V so you need to wire 4 of them in series. Each cell has 280Ah capacity, so only 4 cells will do.
With Lithium-ion, each cell generally has a much lower capacity so you need to run multiple cells in parallel, and joining these into series to make for the 12V. Also, unlike LiFePO4 which is 3.2V/cell, Lion = 3.7V, so slightly more off 12V (4×3.2 = 12.8V)
And you need to have (or have access to) a spotwelder to create proper connections on Lion-cells….

The LiFePO4 cells however are much easier to use: Just a ‘block’ with M6 inserts, and included busbars to connect them in serie.
And, when sourcing them directly from China, they are cheap: $80 / cell. So for $320 + shipping you will have 12.8V / 280Ah.
Besides the batteries, you also need a BMS (Battery management system, more on that later)

I only have to replace the charger (Which I was aware of).

Lead-acid batteries require a slightly more advanced charging profile than LiFePO4. A decent lead-acid charger will periodicaly equalize the cells using a higher voltage, primary to remove sulphation on the plates in the battery. However, this voltage is way too much for a Lithium battery, so this will overcharge them!

During initial charge, the charger will start with providing its maximum current (Bulk stage). This continues till the battery voltage reaches the absorbtion voltage. Once the batterie continues to charge, the current drops. If the current is below a certain point (or time, depending on the charger), the battery will hit its float stage, and the charger only provides a lower voltage to maintain this SOC (State of charge). This is 3-phase charging… Fine for lead-acid.
More advanced chargers include more stages, eg equalizing. This can’t be switched of on all chargers, so you have to be carefull when upgrading to Lithium. Also, not all chargers can set to various voltages. ‘Wet’ lead-acid batteries have slightly different voltage requirements eg compared to Calcium-based batteries.

Also, while a lead-acid battery is limited in its charging capacity (generally recommended to have 1/5 C charging rate, so 20A max for a 100Ah battery), LiFePO4 can handle much larger charge currents (and discharge currents as well). So you can charge the battery much faster (although this slightly decreases its life if you charge it really fast).

Anyway: 280Ah with a 10A charger won’t really do, so I needed a bigger charger.

Since I have also DC-DC charging from the alternator (40A) and solar (about 25A max with optimal sun) I didn’t want to spend a whole lot of money on a charger which I’ll probably use occasionally. So: No expensive Victron or so for me 🙂

I only just needed a ‘huge power brick’. So unlike the well known RV charger brands like Renogy, Victron, Ctek and so on, I went to the industrial market: This also uses batteries for various purposes. And as with a lot of stuff: Anything labeled ‘Campervan’ is way overpriced.. (This surely applies to most electrical stuff: Campervan electrics are overpriced, you can get the same quality or better at a marine hardware shop: Boats are using low-voltage system for ages, while campervans are ‘the new kid on the block’ where they can charge you 200%…

So I ended up at https://www.meanwell.com/, a well known brand in power supplies and similar stuff. On their website I found various chargers.
So I found the Meanwell PB-360. This is a very nice, robust charger, aluminium cased, and able to deliver 24A of charging. And its only 3-phase, so will work fine for Lithium. (Note: Not all datasheets of this model include Lithium, but it does work fine, and later datasheets do list it).
It was affordable: 100 euro ($120 or so) and the output voltage can be adjusted to some more conservative settings to increase the life of Lithium even more (more on that later).
Also, the absorbtion stage is not time-based, but current based. So no overcharging, it will go to float automaticly.

Ceiling

The ceiling is insulated with PIR plates, as explained in Roof, insulation, installing vent, fan and solar.

The top of the PIR boards are covered with self-adhesive Armaflex sheets (9mm thick).
With this, the insulation was equal in thickness to the support beams, and the wooden timber which I had previously installed. The Armaflex was already black, the wooden timer and everything else have been spraypainted black to make a rather solid black background.

On top of this, there will be a layer of black fabric. I found a cheap black fabric (2.50 eur / m). This is slightly stretchable, perfect for my purpose. Since this is rather thin, white spots might be seen through the fabric, thats why I made the ceiling black and spraypainted where needed.

Once cut to size, I used thumbtacks to temporary fix the fabric in place.

The final cladding will be made from slats of beech wood, just as the countertops and table. Also painted in the same color. The slats were 4.5cm (1 3/4″) width and 1cm (3/8″) thick, I used a wood planer to remove 4mm and make them 6mm (1/4″) thick (Save weight, gain usuable height).
After that, I’ve sanded them down, and painted them with dark varnish.

Once the slats were finished, I started installing them to the ceiling. The center slat also contained the lights, so I had to cut the appropriate holes first. Once confirmed everything was fine, I nailed them to the wood structure of the ceiling (About each 25cm / 10″), using a pneumatic stapler (which only created very small holes, barely visible).

I used some leftover wood of 12mm (1/2″) as seperator between the slats, exposing the fabric. Used this as spacer for equal with along the slats, nailed them and went to the next one. The fabric gives it a nice smooth backdrop. And once more slats are installed, I removed the thumbtacks, and the fabric is hold into place by the slats.

Electrics – Part 2

In the previous part, I described my primairy circuits (for all charging options and high-current stuff).

In the schematic, there is a 12-port fusebox. All general items are connected to this fusebox. In this post, some more information about all items connected.

I have a bunch of 12V items, which require separate circuits (or at least, I wanted).

  • Maxxfan
  • Waterpump
  • Webasto diesel heater
  • Electric boiler (water heater)
  • All LED lights
  • 12V outlet near the bed
  • 12V outlet in the kichen area
  • 12V outlet near the side door
  • Refrigerator
  • Bed system

For the LED lights, I added a stablisator. This has 8-40V input, and a 12V output, rated for 10A. (All lights on maximum power draw around 6.5A)
I did so, since the voltage in the van can vary, depending of the battery state. During absorbtion, it will go up to 14.2V, which is a 20% more than the LEDs are rated for. This definitely won’t increase their lifetime, so it’s easy and to be on the safe side, just add the regulator (its about $15 or so on AliExpress). Replacing lights will be PITA 🙂

In the van, I have plenty of lights. In the ceiling, there are 3 led spots installed, each 3W.
Below the cabinets, I’ve installed 2 LED strips, 1 in each cabinet, running the full length. (In total around 3.5m length). I used high power LED strips, so when needed, I can put them on full power.
Both strips are indepently dimmable using small soft-touch dimmers. Also the ceiling lights are a separate dimmer/switch.
On the cabinet above the cabin and on the panel in the back, I’ve installed RGBWW LED stips. Besides a normal white light, they can have any color.

On the bed area, I’ve installed 2 small 3W led spots, 1 for each bed. These can be used as reading light, or spotlight when needed. Just simple on-off switch, which was factory installed in the base.

All 12V outlets are the regular sigarette sockets. I simply plugin a car USB charger to have USB sockets for phone and so on. No fixed USB, just replace the USB car charger to whatever USB you require. With all the various standards, and evolving techniques, I can easily upgrade to USB-C, QC 4.0, or whatever will come in the future. (Unlike fixed USB chargers)

Electrics

Now it was time to start with the electrics. My setup will exist of 2 parts:
The battery and the high-current / charging stuff in the back (Chargers, inverter, main fuses and so on).
Under the bench in the back there will be a seperate fusebox for all the regular uses (Fan, lights, refrigerator and so on). With this, I was able to keep the high-current wires as short as possible.
For initial testing and build, I bought a small 105Ah lead-acid battery. I’ll replace this soon with a DIY build of 280Ah LiFePO4 (Lithium) batteries.
My setup is already suitable for Lithium (Except for the charger at the moment), so no major changes are required once the batteries are finished and installed.

Charging will be done in 3 ways

  • Using solar: I have a Denim 315Wp panel on the roof, and an Epever Tracer 3210AN solar charge controller
  • Using the alternator: I have installed a Renogy 40A DC-DC charger. This will limit the current draw from the alternator to approx 40A and will have proper charge characteristics for Lithium (and for now lead-acid)
  • Using the grid: I have installed a 10A charger (Will be upgraded once the Lithium will be installed)

The inverter is a Xenteq 1500W inverter, pure sinewave. Nowadays, pure sine isn’t that much more expensive than a modified sine wave, and I prefer to have a good clean power, so didn’t go for a modified sine wave (Which sometimes can cause problems). Also, with the 1500W I have plenty of power to run some equipment with a higher current draw.
(But for now I’ll limit this, since the 105Ah lead-acid doesn’t like these huge discharge rates).

For the main cables I used 50mm2 (1AWG) to be able to run the inverter without too much cable loss and heat. All cables are connected using cable lugs, covered with heat shrink.

I also added a switch to be able to disconnect everything from the battery at once in case of emergency, or eg when the van isn’t used for longer periods (To prevent flattening the battery eventually)

For the lights, I’ve installed a seperate 12V circuit, powered by a 12V regulator (a 10A buck/boost regulator, 8-40V input, 12v output). Most of the lights are made for 12V. But in a car/van, the voltage can be anywhere between 10 and 15V, depending on the battery type and SOC (State of charge). Since 15V is about 25% over its 12V rating, I didn’t want to expose my led lights to this (preventing premature burnout).

Everything else is directly connected to the fuse box (Maxxfan, boiler, diesel heater, refrigerator, waterpump and so on)

Unlike a lot of vanbuilers, I didn’t include any USB sockets in my van. Instead, I used the regular 12V outlets (cigarette lighter sockets)
Why? Since this is more future proof. A few years ago you needed a 5V 2A to charge your phone. Now, depending on the phone, you need QuickCharge for example, while other phones starting to adopt USB-C. The demand for power continues, and the technology continues evolving.
Having fixed USB ports would limit the usage to the system installed… Having a 12V socket allows me to simply upgrade the charger to whatever is needed at that time / whatever device I own.

I also installed a small 6 litre boiler for heating water. Yes, this draws a lot of power, and is not really recommended, especially with the 105Ah lead-acid battery. It will drain it pretty fast, especially with lead acid, where only 50% of the capacity is actually usuable (unless you’re willing to kill the battery, or at least shorten its lifespan significally)
But with the amount of solar, I still can run it, and power it on when needed.
Once the new lithium battery is installed, it won’t be less of an issue.

Building cabinets

Building the cabinets took the majority of the time. I had made some quick drawings of the design I had in mind: A fixed cabinet as kitchen, 2 closets (left, below the sink) and right, below the stove. In between I wanted to have 3 big drawers. Also, I wanted to have a fairly decent sized countertop, not the usual very small campervan ones. Also, I didn’t like the looks of the commercial available stove/sinks. I preferred a more modern, more house-style look.
For the sink, I took an small sink from Ikea, the Boholmen sink, https://www.ikea.com/nl/nl/p/boholmen-inbouwspoelbak-1-bak-roestvrij-staal-s99157501/
This sink is designed to be mounted in the countertop, but I am going to install it below it.
This will give the sink about 3cm more depth (since it’s below the wood), and allows me to use the leftover piece as a plate to cover the sink when not in use. (Thus providing more space).

For the stove, I found a nice, but affordable stove at Klarstein ( https://www.klarstein.nl/Grote-Huishoudelijke-Apparaten/Kookplaten/Ignito-Domino-gasfornuis-2-pitten-Sabaf-brander-glaskeramiek-zwart-Zwart-2-branders.html )
This was a 2-burner stove, with black glass cover, so very nice looking.
Originally it was for use with natural gas, but I’ve changed the jets to match the van’s gas (Propane)

Above the kitchen, I wanted to have some storage space, with integraded LED light stip in the bottom.
On the other side, next to the sliding door, I wanted a cabinet with 2 drawers, the bottom one will hold my refrigerator. I decided to go for a fairly small cooling box since this was much more affordable. I have bought the Mobicool FR40, a 40 litre refrigerator box. Compressor based (I didn’t want to go with absorbtion due to the high amount of power required, and I didn’t want to run it on propane). The countertop on this cabinet will be equally in heigh with the main countertop, providing even more space.
Between the bed and the cabinets, I wanted to have a seating area, so 2 people can easily sit across eachother. In night mode, the bed will slide out, using these 2 seats as support.
Just below the bed, a retractable tabletop is installed.

Also, there will be more storage above this whole part of the van. I didn’t want to extend the cabinets from the kitchen all the way to the back, since leaving it open gives more ‘feeling of space’, and I won’t bang my head against the overhead cupboards 😉

All cabinets are made of small (22mm x 32mm) pine battens. Using a pneumatic stapler and wood glue I have build the structural frame. All panels are made of 9mm plywood, the doors and front panels of the drawers are made of 15mm thick plywood.

For all panels, I didn’t go for the mostly used birch plywood. My local woodshop (I don’t buy wood at the DIY stores – Way overpriced and crappy quality) advised me to use Tipoply (some brand name), based on poplar plywood.
I looked for its specs, and its weight is almost identical to birch plywood, but it was a lot cheaper (I payed about 19 euro for a 9mm 244 x 122cm piece)

The doors on the upper cabinets are build of 15mm plywood, the center is cut out with a jigsaw, edges are rounded with a router. On the back, I’ve added about 5mm additional space with a router in order to fit a 12mm panel in. I used the router to remove this 12mm, creating a 3mm thick outer ring to glue the 12mm panel on, to give the ‘recessed’ front look.
All front panels (both cupboards and main cabinets) are made from 1 single piece of wood, carefully creating all holes and cuts.
On the main cabinet (the kitchen), I’ve added a 8cm tow kick.

Once the frame was stapled and glued, I covered the small holes created by the staple gun, sanded, primed, and painted (multiple layers of paint to give it a decent look). This took quite some time!

I also builded all the drawers, painted them and installed the sliding rails (with softclose).

For the countertop, I took a big beech wood panel from a local DIY store. Unlike most of the other plywood, this was a quite heavy piece of wood, but since my van is capable of a total weigth of 3500kg, and I did like the looks of this, I just took this panel.
From this I have cut 3 pieces: The countertop, the top of the smaller cabinet and the sliding table. So it will all look identical.
I’ve painted it with a rather dark vanish, Rambo Pantserlak Puur Palissander, Used 3 layers to give it a dark wood tint, while retaining the original wood structure. Between layers, everything was sanded to give it a nice smooth finish.

The handles are from AliExpress. The hinges for the doors are from Ikea, ( Komplement, soft-close, 4 pieces for 14 euro). The hinges for the upper cabinets are from DGN in Italy (I ordered them directly at the factory). Those are nice solid hinges, which don’t need additional support to keep the doors open, and the opening angle can be adjusted). And they were cheap, about 3.5 eur/piece. I saw those hinges at the CaravanSalon last year, so I knew I wanted those (DGN 2960)

Walls, weelarches and bulkhead

It was time to start the construction of the walls. Since I was planning a sideways bed in the back, I had to pay attention to the final remaining space. The Ducato is 200cm (78″) between the outside panels, I didn’t want to loose much space.
For the lower parts, around the wheel arch, this wasn’t an issue.
I removed the small supporting piece of steel to get a flat surface on the upper part. Since I wanted still some minimal level of insulation (It will be the bed area) I covered it with 10mm Xtrem. This also prevented the panel from rattling and gave it some level of protection and stiffness. On top of the Xtrem I glued a 3mm thick PVC panel. This acts as a protection, and will evenly distribute any punch loads. (I didn’t want the thin panels left alone, very likely to make small dents in it)
The final panel is covered with 4way stretch lining carpet to give it a nice finish.

The lower parts are filled with some remaining pieces of PIR insulation to cover the big parts, everything else was finished with sheep woll as insulation. When needed, I also installed the wiring, before covering it with a final sheet of plywood.

On the wheel arches, I used Armaflex to insulate those, build a frame using some slats, filled it with sheep woll and covered it with plywood.

In the back, I also made a small closet where the gas bottle will be installed. This one has been properly sealed using glue to prevent gas leakage. It also has a vent in the floor for any leaking gas.

In the front, where the old steel bulkhead used to be, I installed a new frame. This will be the new separation between the cabin and the living space. It is installed about 10cm more to the back, to cover for the curve the old bulkhead had (In order to fit the backrest of the seats).

Roof, insulation, installing vent, fan and solar

Once the floor was finished I started working on the roof and ceiling.

The holes were already cut, now it was time to install the vent (Fiamma Vent 40) in the front, and the Maxxfan in the back. Also, I had to drill a hole for the cables of the solar panel, install it’s cover and install the panel.

I’ve measured the layout and made sure I (just) had enough room for everything: The solar panel fits perfectly between both holes.

For the vent and the fan, I first had to made a support bracket on the inside. Used Polymer adhesive to mount this. On the outside, I made small pieces of an old Trespa board to cover the roof, making it a rather flat surface so I could fix the fan/vent.

On the inside, I have glued small slats of pine. This will support the final ceiling, so I installed them from left to right, each approx 30cm apart, so the final ceiling has plenty of support.
However, since the van is slightly curved, this job was taking some time. I had to cut each slat with a jigsaw for about 80%, repeating each 2cm, in order to make the wood easier to bend and follow the curves of the van. So.. with 8 pieces, 40 cuts each or so..
Created a small ‘tool’ from my jigsaw so I just could slide it in to get all incisions.

For the solar panel, I used a regular panel. They are much cheaper, and the long-term reliability of flexible panels is questionable. (Lots of people are reporting issues after a few years). On the roof, I glued 6 support brackets for the panels using Sikaflex 552AT.
I didn’t use screws. The Sikaflex has massive strenght, so no need for screws and/or take the risk of potential leaks.
I didn’t doubt the Sikaflex, if anything, it would be the paint. So I made sure everything was cleaned properly, used primer, and to be on the safe side, I sanded the paint on some small spots so the Sikaflex would stick to the bare metal (This was only done on the inside, the brackets had plenty of surface, so I made sure there was at least 1 cm additional adhesive with paint, didnt want to expose the bare metal to the elements off course.

Both the vent and the fan are glued with 1 layer of Polymer on the inner side (this is strong stuff), and 1 stripe of Dekaseal 1512 on the outside, making it waterproof. So even if the Dekaseal somehow fails, there is still an additional layer preventing water to come in.

Also glued the cable entry to the roof. This could fit right underneath the solar panel, so highly unlikely any water could come in!

Once everything was installed on the roof, I finished the inside of the ceiling, yet again using PIR plates. Since the ceiling was slightly over 2cm in thickness, I covered the PIR plates with 9mm Armaflex for additional insulation and to equalize the height to the support beams om the van.

Also installed the wiring for the Maxxfan and the ceiling spots in the ceiling, before finishing the upper layer with the Armaflex.

Installing power hookup, fixing sliding rail

On the outside of the van, I needed an electrical hookup.

Most campervans in Europe use a 16A CEE plug, but I didn’t like those (too big)

CEE connector

Since I was planning on installing solar and a DC charger (using the alternator to charge the leisure battery) it was likely I wasn’t going to use it frequently, so I wanted something less visible, smaller, and it would save me cutting another hole in the van.

I decided to go for a DEFA connector. Lesser know in the Netherlands, but more common in eg Scandinavia, where it’s frequently used for eg engine heaters during wintertime.
Smaller (very small compared to the CEE plug), but still suitable for automotive usage, and rated for 16A current. It is also used on service vans, but not so much on campervans.

I bought a set (Cable and connector). Pretty expensive, although I found a nice deal online from someone in Lithuania.

DEFA connection kit

I found some available space behind the fuel cover where I could fit it. When using the cable, the fuel cover has to remain (partially) open, but as stated, I’m not likely to use it frequently, so it will do the job. And it’s small and stealth 🙂

Fixing the sliding rail

Once that was installed, I had to check the rail of the sliding door. On these vans, this is a known issue: The sliding rail is made from RVS, while the van is metal (painted). Water will stay between those, causing rust. Since the nuts from the rail are on the inside of the van, it’s hard to reach once the build is done.
I’ve removed the rail, and surely, there was some rust. So I cleaned it, repainted it with anti-rust (Hammerite). I also added a slice of rubber, so there is a rubber gasket between the rail and the chassis. Not likely there will be any water soon.
For the rubber part, I bought a cheap bike tyre, which I cut open and made a nice strip of it.

Another job done 🙂