Thanks Michael. Good observations. Makes one wish they would build these vans with a vacuum chamber between the inner and outer walls! I'll do my best, but I for one am learning to accept that sometimes in summer it's going to be hot, and sometimes in winter it's going to be cold.
A timely addition to Gary's recent tests. It certainly has implications for folks using metal framing (80/20, etc) inside their vans. Those framing with wood, less so. But any exposed interior body metal is always an issue. Most don't like to sacrifice interior space to insulate the inward faces of the van's metal ribs. But a thin cover of wood or carpet (etc) will at least make it more comfortable to touch. I don't insist on perfect, but it helps to know there are things that can be done without overly compromising budget or interior space. Example: When I recently bolted Unistrut channel to the metal floor for a structural anchor, I put 1/8" sill-plate foam under it to interrupt thermal bridging a bit.
Iffy infrared (IR) photo as I hacked an iPhone5 sensor onto an iPhone7.
There was an obstruction to heater airflow guiding some airflow across the uncovered main pillar, so that's the hottest portion of the photo... well, except for the drivers' window showing it was down two inches.... This is a window van, but glass will not transmit IR through it for the camera so the image show only the outside temperature and even that is screwy as the smooth surface plays with IR observations.
Anyhow - if we want interior warm/cool stability then stand-offs, cross-firring AND perhaps extra insulation over thicker metal stampings wherever possible since it conducts proportionally more...
I just wanted to give some extra depth to Michael Dew's post (thanks MD).... ISO is the foil-faced polyiso foam sheathing, R3 = 1/2" sheet; 1/4" stuff is Prodex held against glass by magnets around the edges onto window frames... I'll do a decent thread write-up soon.
I also live in Vancouver, I haven't insulated my ProMaster yet, but I had fairly good success avoiding this issue on a previous build. I spray foamed a van and used high quality adhesive backed foam tape that I purchased in rolls from "Cascade Aqua Tech" a window glazing supply store in Burnaby. I used the tape on any areas that I needed to attach wooden studs, (put the tape behind the studs) The only problem I had was where I has some metal electrical boxes, they were so close to the exterior wall, that they turned into a heat sink. In the future I would only use plastic single gang boxes. Home Depot sells a similar product, but a much inferior product, both the density of the foam and the adhesive is inferior.
Promaster is my 5th conversion, First one was in 1995 and it even had Solar on the roof, and a few years later it had LED lighting!
Black vans are tough to keep cool. No amount of thermal isolation is going to fix that. For dark colored vans, we recommend a layer of Low-E on the roof (after Thinsulate) and possibly the walls as well.
I built our first van in the eighties and it didn't have any insulation other than the shag carpet on the walls and ceiling. We enjoyed that van just as much we do our current vans. Don't beat yourself up about insulating. Let us help you choose appropriate materials and make practical decisions about your build based on your needs and abilities.