...even more questions ?!...and some progress

I would have put a ceramic paint coating on every surface that is exposed, using that as a thermal barrier to reduce heat transfer from the outside to the inside during summer and from the inside out. Those other products don't adhere to the surface well enough to be as effective as a 1mm thick coating that goes on liquid.

The other thing to consider is an additional thermal barrier before the insulation, this can be the bubble wrap stuff but an air pocket is needed for that. Once the thermo bleeding is stopped, then sound deadening and insulation (two different animals) can be applied.

 

I’ve thought a lot about all this for my Truck. The dyna mat you already did is good for noise caused from vibration. Often used in cars with the big bass sub woofers. That’s stuffs heavy. The next layer should be a thicker less dense and lighter weight closed cell foam. It will insulate and due to thickness absorb noise as well as it travels. Needs to be self adhesive, or glued in place to avoid condensation. Condensation is the problem. Insulation either needs to breathe or be totally contained. Any layers that aren’t glued together will get condensation between them. I read on here somewhere about using a refrigeration product like armacell. It can be bought in sheets at hvac suppliers. Depending on cost. Might be the best product. Same stuff used on home a/c lines. Only sold in sheets. I made the mistake of layering rubber matting on my floor, under the factory foam. Made my floor perfectly flat and even. The problem is moisture between every layer. Imagine a cooler ice cold inside, warm outside. No air between surfaces. That’s what you want. Just my thoughts. Interesting post. Looks like a good start. Nice Truck.

 

Pav, yours hands on I didn't know. They claim my Peterbilt is insulated but I'm not buying... LOL...

Looking forward to hearing about the results...

They "say" the insulation is good for both summer and winter...

Any word on the APU?