Similar to you, I read the various threads on insulation and methods - the ideal solution for keeping heat out is not always obvious (to me)
The metal structure in the vans really makes insulation and fit out - challenging.
What would be really nice is if these van mfg companies would make the body from fiberglass or carbon fiber, like an RV. This would rather dramatically reduce noise and thermal conductivity. I have even considered buying an empty shell of a small class C for this reason. If I could find one that doesn't look like a class C so I could park it in front of my house, I would do it.
As far as your insulation plan, IMHO, the approach needs to be kept as simple as possible, and use an insulation that is at least somewhat flexible / bendable. I have read that the thermax insulation is the highest R value per inch, but I remain concerned that it will squeak. I would expect the same from the menards product.
So far, I haven't seen any approach that looks all that much better than just filling with mineral wool and covering the interior with 1/4 inch of baltic birch ply. "Maybe" a continuous layer of a foam pipe insulation under the ply.
The exception of course is if you are willing to put in insulation that is substantially thicker than the wall cavity. I was in a van that had 4 inches of insulation and it was surprisingly cool on a hot day. I don't like the stuff, but it was the blue jean insulation.
It won't take long for other forum members to make improved suggestions over mine.
IMHO, if you think that you will need air conditioning, you do - so just skip the fan and go straight to A/C.
Some experience with auxiliary power
Last edited by harryn; 08-18-2019 at 12:19:AM.