some expanding foam will work you just have to know right where to spray it. I would suggest dynamat it can be pricey compared to others but it works so well. if you have the money you should definately get some dynamat extreme.
I remember back in the day (mid 80's) if we wanted our sh!t to be louder we put the box in the back seat, lol! You could but a sealed box with two 18's in the back seat of a fleetwood with ease, mannnthose were the days...
Ha... I wuz jus bein born in the late 80's, I might give it a shot jus to see what it will sound like... Jus with it bein in my trunk, if someone with long hair sits in it their hair will move, and it would really move with my box in the back seat!! Ha that gives me a project to do friday. Ill let ya kno how it works out..
i got like 3 gal of edead V3 in my whole car and it worked real well (everything is blue thou--but they have black), but expanding foam is very very good if you can find where to put it and put it there, only like 5 bucks a can too
i used like 3 or 4 cans but wear gloves, i couldnt get that crap off for a week, and i flung some in my eye, i thought i was gonna have to go to the hospital but lukily it landed square on my contacy and just runied it instead of my eye, god it hurt thou, so watch out for that.