When I did the inside of the 66’ Barracuda I used two boxes of this stuff from Amazon.
I also only did the floors, roof, inside of doors and inside of quarter panels but inside the car only. I did not want to see the product if I opened the trunk. Works good but I am worried now about if the car gets too hot and will it fail inside the roof.... on my new head liner.
Glad I installed ac.
Kilmat 80 mil 36 sqft Car Sound...
https://www.amazon.com/dp/B0751CBXBT/?tag=fabo03-20