my sub is a square heavy box it fits convienently up against the hole where you fold the seats down in my 2001. since before this day i have just let it sit on my spare tire, i dont have a cadboard floor or anything just the carpet and it would roll or move around before but today i finally climed in my trunk and i put 4 radio backstraps to the box, 1 on each side drilled through the carpet between 2 wheel wells no gas tank and 2 on top to a hollow painted body peice. after driving 30 min the screw up top started coming loose and i could here it shaking metal to metal so i went back to my screwdriver and tore a peice of towel folded it and slide it between backstrap and car, screwed it back in and thats how it is now, but i have a feeling this wont be too permanent, there are so many other rattles i gotta stop now

 

Uhh...something isnt right if your screws unscrew themselves out of metal. How many screws did you use? Use some lock washers and/or speed clips on a couple screws per backstrap and they shouldnt come out.

 

Lock washers, use L- brackets 2 per side, two on the rear should more then be enough. The sound deadning process is a royal pain in the ***, have fun.

 

See link in sig for an option.