I use lizzard skin in every nook and cranny I could reach while the car was on a rotisserie. Under side of the roof , up in the wheel wells entire underside of the car too. Foamed all the pillars and everywhere else I could foam that there wasn't need for room for something. standard pad under the carpet. This car is VERY quiet. I run a 2 3/4 exhaust with Dynomax VT mufflers. SUPER quiet at cruise, and very nice when accelerating.
I realize this is not practical when not involved in a full on restoration but I like posting this because the question comes up A LOT!!!!!!
The lizzard skin seems expensive but it really is less than any other method for sure when you consider where you can spray it that you would never be able to apply any kind of peel and stick type product.