That extra adhesion time doesn't really get you anything. All of these products have sufficient adhesion to get the job done. Butyl mat's adhesion strength actually increases with time. I'll be making this clearer in the new version. I was trying to figure out why asphalt mats failed so often and peel strength seemed to be a logical place to look.
The air inside your trunk probably will not get to 160°F, but the sheet metal almost certainly will - especially South of the Mason-Dixon line. It doesn't even need to get that hot. The rubber compounds that stabilize the asphalt start to deteriorate at temperatures much lower than that. Asphalt products become more prone to failure with the passage of time - may not fail during the first or second year, but may well during the second or third.
FatMat is Peel & Seal, or so similar that it is impossible to tell the difference. In terms of effectiveness, it is impossible for asphalt to work any where near as well as butyl. Both butyl and asphalt damp vibration by adding mass to the panel. They may also stiffen the panel, depending on thickness of the foil and strength of the adhesive. Butyl has the advantage of being viscoelastic which adds a completely different mechanism that asphalt doesn't have. FatMat is much lighter than the others, so even in terms of mass, it loses.
There is no reason to use asphalt in a car. I wouldn't even consider it. Since butyl works so much better, just spend as much on it as you were planning to spend on asphalt. Spread the stuff out and you will never have to worry about it again.
