Diy Promaster Camper Conversion Guide – Part I

  • by Thomas Gagnon
  • Dec 28,2020

This year my husband Joel and I decided to do something crazy and head out on a 2-year long road trip through Central and South America. We were super excited for this trip but we had one problem- no transportation.

We recently sold our converted Honda Element camper suv in order to get something bigger for the long trip.

With a tiny budget and not a whole lot of money, we couldn’t afford to spend our entire savings on buying a decked out $100k+ camper van so instead we decided to put our own brains and hands to work and do our own awesome DIY custom camper van conversion.

awesome DIY homemade promaster campervan conversion

We found the perfect, slightly used Ram Promaster van for $20K and over the next 3 months converted the blank cargo van into a fully livable custom built camper for just under $3k in conversion cost.

Our guide below covers exactly how we did our DIY camper conversion for anyone inspired to join the van life movement themselves on a low-cost budget.

amazing DIY custom promaster campervan conversion

To make this Promaster camper van conversion guide easier to follow, we divided our how to guide into two parts. Part I will cover the conversion planning, layout design ideas and all of the prep work we did that’s not necessarily visible but make everything work. Part II will cover the construction of the finished product and any extras we added to make our van life travel on the road more comfortable.

Promaster Campervan Conversion Guide-Part I

1. Layout & Must Haves
2. Installing Windows & Fan
3. Wiring & Electrical
4. Insulation

1. Layout & Must Haves

When we bought the Ram Promaster van it was an empty room on wheels so the first task of our van conversion process was to come up with some campervan conversion ideas.

van to campervan conversion ideas

During our research, we couldn’t find any low-cost Ram Promaster conversion kits so we had to create our own customized layout and plan from scratch. After all, one of our main goals was to keep our van conversion cost as low as possible and we also liked the idea to have the freedom to modify anything in our van to make it look amazing and unique instead of using a generic kit.

Some of our DIY van conversion must have requirements were:

  • Permanent bed with storage under the bed
  • Fridge
  • A kitchen area with permanent cooking stove
  • Sink with running water
  • Sliding windows for light and air circulation
  • Fan in the roof
  • Space for our cat
  • Swivel seat for the passenger

promaster campervan conversion layout plan

We had a basic idea that we wanted the kitchen to be in the front against the left wall and the bed in the back. Everything else we had to figure out as we built the van.

2. Installing Windows & Fan

Before we started with any interior work, the first task was to cut out holes in the van for the windows and fan. This was actually one of the scariest tasks to do because if something went wrong in this step, the van would be ruined. Sounds fun, right?

DIY promaster campervan conversion window cutting

To install windows and a fan, you’ll need:

  • As many windows as you’d like to add
  • An RV roof fan
  • Black butyl tape
  • A jigsaw with a metal blade
  • Paint to touch up the cut edges

We wanted to install two sliding windows in our campervan to allow air in, add better vision and circulate air for cooking. We wanted to add one window on each side, one on the sliding door and one behind the driver’s seat.

used campervan conversion installing windows

The sliding windows we chose came in medium size with screens to protect against bugs at night. We bought the windows from a local RV surplus store instead of going with the windows that are made specifically for Ram Promasters by CR Lawrence. The RV surplus store windows cost only $30 each and came with screens and trim rings compared to the others that cost around $500 a piece.

DIY promaster camper van conversion cutting roof for fan

Besides cutting two holes for the windows, we also cut a hole in the roof for the fan. We decided to install the fan towards the back of the van above the bed to get better circulation as the air comes through the sliding windows in the middle of the van and out the fan in the back.

DIY promaster campervan conversion installing ceiling fan

We used a MaxxAir RV roof fan with multiple speeds and a temperature sensor that can be set to automatically turn on the fan if the van gets too hot.

We used a jigsaw to cut the hole for the fan and a hole puncher powered by compressed air to cut the window holes. The hole puncher left a smoother edge and less fine cuttings which tend to dig themselves into the paint and can cause tiny rust spots to appear.

how to install RV windows in promaster van conversion

When installing the windows and fan, we touched up every cut edge with white paint so it wouldn’t rust and used this black butyl tape to seal everything off from water leaks.

Cutting all three holes right after purchasing the van was intimidating at first, but after making the first cut it didn’t feel so scary after all.

3. Wiring & Electrical

We are not electrical engineers so at first wiring seemed pretty intimidating to take on, but it turned out to be a lot simpler than we thought.

promaster campervan conversion guide wiring

To do the wiring part of the conversion you will need:

  • 1 or 2 deep cycle batteries
  • Battery isolator relay
  • Fuse block
  • 2 different colored rolls of 16 GA cable
  • 2 different colored rolls of 12 GA cable
  • 1 roll of 6 GA cable
  • Pack of 12V switches from Amazon
  • LED lights
  • LED String lights (optional for decoration)
  • Wire cutters/crimpers
  • Wire connections


  • 1-2 solar panels
  • solar charge controller
  • 10 gauge cable
  • inverter

The first step is to draw a diagram of your electrical system.

promaster campervan conversion simple electrical wiring diagram

Our electrical system would include two deep-cycle Group 31 batteries (our “house” batteries) being charged by the car’s alternator while driving and a single solar panel on the roof. This system will easily power our LED lights, fridge, and water pump and have extra juice to charge our camera gear and computers.

Instead of installing an expensive pure sine wave inverter to power up our electronics, we just bought car chargers for the few things that aren’t already powered from a USB drive.

how to wire promaster van for vanlife travel

We used a battery isolator relay to charge the two house batteries from the car’s alternator while driving but disconnect them when the car is off, preventing us from discharging the main car battery and getting stranded in the middle of nowhere. This system worked great on our Honda Element conversion as long as we turned on the car for at least 15 minutes a day.

how to install house batteries promaster campervan conversion

The two house batteries were placed in the rear of the van between the rear wheel wells to distribute the weight to the back a bit. This location worked out great because we could easily place the fuse blocks and solar charge controller right above it and have easy access to them in case something goes wrong.

promaster campervan conversion tiny budget

For the batteries, we used two deep-cycle group 31 batteries from Pepboys that seem to always be on sale for around $50 each. They are regular lead-acid batteries that could potentially release harmful gasses so they need to be in a sealed compartment. We created the sealed compartment using 3/4” plywood and high-density foam weatherstrip between the lid and the box, then used a ¾” hose vented to the outside right below the taillight.

ram promaster van conversion lights

We used LED lighting all throughout because they are really efficient and don’t get hot like regular lights do. For when we need bright lights we installed five really efficient and bright LED puck lights on the ceiling and for when we want mood lighting we hung dimmable LED string lights all around the van. We used the 6th puck light under the bed in the rear storage compartment.

how to install solar panel promaster campervan conversion

We also decided to add a solar panel on the roof of the van to help keep the batteries maintained on sunny days when we don’t do a lot of driving. Adding a solar panel is extremely easy and just needs two more components: a 12V solar panel and a $20 solar charge controller. We found a used 145-watt solar panel for practically nothing on Craigslist and installed it on the roof, then drilled a small hole on the roof to run the two wires in and sealed it with a self-leveling sealant made especially for RV and van roofs.

4. Insulation

Before building up the interior of the Promaster van we wanted to install insulation to keep the van cooler in hot temperatures and warmer in cold temperatures.

Out of all the insulation types, we decided R-max polyiso rigid foam insulation board from Home Depot would be the best fit for our van conversion because:

  • It’s mold proof so it doesn’t need a vapor seal
  • it’s non-toxic so it doesn’t need to be completely sealed off from the living space
  • it’s rigid so it won’t shift or settle down with vibration
  • it has the highest insulation value per inch of thickness so we can maximize interior space

The only downside to rigid foam insulation is that it takes a while to cut and fix into every panel, but considering we don’t need to seal it off completely, it still takes less time than insulating with soft fiber insulation.

van conversion process ceiling insulation for promaster

What you’ll need to do the insulation:

  • three 1” R-Max polyiso rigid foam boards
  • five ½” R-Max polyiso rigid foam boards
  • 1 roll of aluminum duct tape
  • 1 tube of foamboard adhesive
  • a box cutter

We bought 1” and ½” insulation panels to use. We installed a double layer of 1” insulation on the bottom wall side panels and 1” insulation on the top back wall side panels to maximize space for sleeping at night.

We then used foamboard adhesive to stick the insulation onto the walls and flexible duct tape to seal around the edges.

promaster van conversion process windows

For the space around the side windows, we cut out 1/2” insulation and covered it in white cloth. This gave the windows a really nice finished look that was much easier to make than paneling.

On the ceiling, we installed 1/2“ insulation during our conversion to maximize standing room for cooking and hanging out. Since we put a large solar panel and roof rack on top of the van that would act as a constant shade we didn’t need thicker insulation in the ceiling anyway.

how to install ceiling insulation promaster campervan conversion

We painted all the ceiling insulation panels white because we were planning to install roof slats and we didn’t want any colors to peek through the slats.

During the conversion’s insulation step we only sealed off the large panels and didn’t bother with the smaller crevices. On our previous SUV camper conversion  we used a foam gap sealant to seal off all the small areas and ended up making a huge mess from the dripping sealant that was impossible to clean off. We found that sealing off every small area doesn’t add too much more insulation value if the big areas are sealed off properly already so we decided it was best to avoid all the hassle and mess.

ram promaster awesome van to campervan conversion

With the windows, fan, electrical, and insulation in place, we were ready to seal it all up and start working on building up the van interior and giving our Promaster conversion a finished customized look.

In Part 2 of our DIY homemade van conversion process, we will go over how we did the camper van’s interior build and all the extras that we added on to our conversion to make our van life more comfortable.

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