Second skin seems to be the best you can get. Dynamat is just expensive. Hell you can get 12 dollar a roll home depot **** that is a aluminum covered butyl rubber. It'll take a few layers but is the same stuff. Something is far better than nothing. Even if you don't have rattles you'll hear a difference.

A single JL W7 should not shake your car to pieces though over time. If its going to rattle it'll rattle from day one. The only thing that will really cause additional rattles is ripping panels on and off.