Inside my 1st gen 4rnnr I used a similar product (butyl rubber etc.) and then covered that with a self-adhesive thin closed cell thermal foam home product that has an radiant-reflective aluminum "skin" on it. I've yet to do the doors, but just doing the quarters so far has made big difference in interior noise. Too much un-insulated roof for there to be much change in thermal performance, but I figured while I was there....
Sounds like I need to do under the rear carpet on both the floor and the wheel-wells, and inside of the tailgate as well.
Later diesel (& maybe all) trucks have the actual firewall made from a laminate of two thin steel sheets with a mass loaded product between them.
