undercoat floor

For sound, I think your best bet is laying a material under the carpet. I can't see any spray really offering any sort of sound deadening. Dynamat is too expensive in my opinion and there are good alternatives out there for much less.

I've actually been looking up spray on bedliners recently for my truck. There was a good review I found on youtube that compared several brands in a durability test. Just FYI, one guy from a body shop told me that the roll on stuff is better and far superior to the spray applications.

Wouldn't it be better to spray under the body rather than under the carpet inside the car? I don't really see what good that would do.