I helped a friend do the firewall and floor in his crew cab diesel once using something similar. I think the stuff he used was called BoomMat...? It was a $100 Amazon splurge for a whole roll and a roller applicator. Can't say much for the changes in heat (it was a black truck, so it was always hot inside thanks to the wide open western Oklahoma skies). However, it did lower the interior ambient noise a bit. Road noise and most of the diesel rattle well dulled out, but you can only do so much for the melodious 7.3 PS.
I would definitely encourage it on the flat vertical panels and doors just to add sound absorbing density and get rid of some of the tin can effect, but don't think that it's a cure-all. Most sound studies recommend a combination of MLV (multi-layer vinyl) plus a jute or closed cell foam to get the best sound and heat reduction.
I went ahead and ordered two rolls. I’m going to use one in a 72K 10 that I’m doing a frame off resto on. and I’m gonna use some in one of my Scrambler’s that has an automatic transmission. Scrambler has just the factory carpet so I’m hoping it helps with heat and road noise. I hate to cover the floor panels in the Scrambler, because they’re completely rust free and in perfect condition I didn’t want to cover that up. My understanding is this is a pretty permanent application.
Thanks for all the feedback, I’ll keep you guys posted.
I have used this on various applications and it takes the temperature down from “ frying and egg “ hot to “runny eggs “definitely worth it but without carpet and poor ventilation , a/c is what really helps especially in Texas