I just recently started my deadening project and only have the trunk done in 1 layer of FatMat, which is just on the floor in the trunk and an entire 40sqft package of Second Skin on the rear panels, wheel wells, underneath the rear deck and inner panels. I will say the SS product cut my hands up, to where the FatMat didn't. SS was a lot easier to mold though and both stick about the same as far as I could tell. I want to do another layer, but I want to get the doors done and the roof and floor. So we shall see after that. Biggest thing about putting this stuff on is it is such a timely procedere.
I say FatMat is fine unless you live in a real warm climate such as Arizona or the likes.