My Promaster Van Build: Rear Entry, Hidden Bath/Shower, and a Few Other Unusual Details

Page 6:  Acoustic and Thermal Insulation, Ventilation Fan and Floor

Not surprisingly, the bare van was very loud on the road. My ears are damaged (tinnitus), so noise is a very real concern; I had to wear sound-cancelling headphones (with music) on the drive home when I first picked it up. I bought a box of Noico sound deadening material at Amazon ($74), and installed it on all the flat body surfaces.

A coverage of 25% or so is considered the most cost effective. This material works by dampening the vibration of the flexible steel panels, which is why that amount is considered adequate. Since the van was also insulated, it’s hard to say how much difference this made, but it seems worth the fairly modest cost.

Here it is on the ceiling. I probably exceeded that 25% minimum. The back middle section of roof is where the fan went.

I installed a 12V Maxxair fan/vent ($195), which is a very popular one. It has several speeds and can be reversed. I am beginning to wonder whether it was worth it. We generally camp mostly in fall, winter and spring, and in the generally cool nights in the West the simple vent in the Chinook was quite adequate. And we have large windows. I’ve only turned the fan on  a few brief times. In retrospect, I’d have run the wiring up there, but just installed a simple vent. But there it is, should we ever need it.

I installed it on the roof with a custom Promaster mounting adapter from ebay ($48) and used 3M Window-weld adhesive to seal it against the roof as recommended. The fan frame is then screwed on, and the screws covered with a flexible sealant.

Here’s a shot that shows part of its wood frame on the inside, glued to the roof. The wire is for LED lights, not the fan, which has a 14 gauge Romex cable.

The next step was insulation. There’s a number of competing theories as to the best way to insulate a van. First off, I should note that these vans are inherently not ideal in terms of insulation, due to their steel framework that creates lots of difficult channels as well as creates thermal bridging. Our 1977 Chinook was way ahead of the game, as the whole rear body was made from a sandwich of fiberglass outside and inside skin with about 3/4″ or 1″ of foam in between. No empty cavities, no thermal bridging. Of course the Chinook’s huge windows were single pane glass, and would get very cold and be dripping wet with condensation on cold mornings.

I’m not going to repeat the seemingly endless debates about the various insulation schemes. There was no doubt in my mind that many of them are too complicated and expensive, and some have very obvious efficiencies.

There’s no question that the most expedient and cost-effective approach is with 1″ polyisocyanurate sheets, which are foil faced and readily available at home improvement centers. Polyiso has an R rating of 6.5 per inch, which is about as good as it gets, and the foil face means that there is no moisture transmission to possibly condense on the inside of the steel walls, from moisture created from breathing and cooking.

 

Spray foam, which highly adhesive, is applied to the back of the boards, then held in place by thin boards that wedged against the opposite side or ridges on the floor or anything else available. In our moist spring air, the foam cures quite quickly.

I’m familiar with working with it, as I’ve used it quite a bit in house insulation projects. I also had a foam gun, which is essential, and they’re not expensive anymore. I think I used seven 4×8 sheets ($220) for the walls, ceiling and floor. And I used quite a few (15 for a total of $136) tall cans of expanding foam to install it and shoot into as many of the channels, nooks and crannies as I felt was worthwhile.

It’s hard to know when to stop. But I know there’s still some more places I could have kept shooting into.  This photo does not show the final result, I shot foam in more of those channels, although I did run some Romex electrical cable and flexible conduit through them first.

I also found that there’s enough room under the factory liner in the small storage nook above the cab to put in a layer of foam. That area can get pretty warm in the sun otherwise.

The next step was to insulate the floor. It’s quite rare to find that in a factory conversion, but it seemed well worth it to me. 1″ boards are foamed to the floor, and weights are placed on them so the foam doesn’t expand.

I cut out channels for two underfloor lines, the far one is for the electric cable from the van battery to where the house batteries will be, to charge them during driving. The near one is for a flex 3/8″ copper tubing to supply the cook top from where the propane tank will be.

Flooring:

I was a bit dubious about Gary’s suggestion to use 3/8″ plywood for the floor, but it’s quite perfect for the job, strong enough and lighter than thicker material. I happened to have a few sheets that I had salvaged from a 1940s house I had remodeled 20 years earlier. It’s from old-growth fir, and is tougher and flatter than the new stuff. I finally found a good use for it. It also got foamed down, on top of the foam panels.

The day I was doing this it was a typical PNW spring day, and the high moisture in the air caused the foam to cure too quickly, which raised parts of my plywood a bit and left me with a slightly uneven floor, which I didn’t notice until later. But since only a relatively small area of the floor is open in the middle, it’s not really an issue and nobody would notice. I did have to shim some of the cabinets a bit.

I hadn’t decided what to use for the finish floor until I was at Costco one day and saw this “coin button” vinyl garage floor material on sale ($177). It was about 50% bigger than I needed, but it looked tough, and it matched the gray used in the van.

I had some foil-faced bubble insulation from a project quite a few years ago, and used it up on the rear wheel wells. I doubt it’s all that effective, but better than nothing.

It’s this stuff. Non slip, and very rugged.

I hadn’t yet trimmed the edges with some aluminum edge trim.

 

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