I've been thinking about this for a while, I never bothered to try, my car is too old to justify anything more than dropping in new speakers. Anyway, since dynamat is expensive, and heavy, why don't people go out and buy that truck bed liner stuff. It's strong, light, and probably cheap. All you gotta do is slop it on yourself. Paint the inside of the doors, trunk, etc with it. Just make sure you don't cover up any weep holds or anything. Way I see it, it should stop rattles, and other probs and It souldn't cost that much. Good idea?