sooo you said you have 4 12s that take 1000 watts im guessing you have some serious amp or amps and a nice HO alternator and a couple runs of 0 wire probably and maybe a couple batteries and you only wanna spend 30 bucks in deadener
come on
only option 2 rolls of peel & seal lol good luck
okay well no i dont have a 4k wattage amp lol i got a mtx thunder 421D its a pretty bangin amp for its size. but ive put a 105 amp alt on it done the big 3 but i used 8 guage for it instead of 0 lol and Worstenemy453 i live in lunenburg County LBC (its a local thing round here) for short lol you?
get a board of 4'x8' 3/4'' mdf. Cut it up, make a false floor out of it. Then add what you can onto the sides/lid/everywhere. For way too tight corners and odd shapes, get some mass loaded vinyl. use some bytl rope along with self tapping screws to hold the boards in place.