well keep in mind like someone said earlier directly behind the seat is the gas tank. and that ive been told that is some kind of boron steel. so it is supposedly really hard to cut through. i know that there is "some" room in that wall for speakers and the only reason i know that is because A. there are already speakers there and B. the roadster roll cage gets bolted in there. but its not to far down from the top of the back wall. i've thought about putting a sub in the first aid kit area as well. and i do know in order to get rid of vibration you need a HECK of a lot of dynomat.