I filled all the voids in mine with great stuff expanding foam from home depot. The sound deadening just didn't kill the rattles. If you do be sure to get the non hardening type for windows (blue can) not the red or it will expand and harden which will possibly deform or cause damage to the metal. Also be sure to just do a little at a time or it can take forever to completely dry. I then covered it in sound deadener.
I get all my sound deadener from a company called Second Skin (www.secondskinaudio.com). They make amazing products and the customer service is second to none...i'm not just saying that. It's a bit pricey, but you absolutely get what you pay for.
I have a rattle with one sub.. Not that bad with normal listening..
But when I turn up the volume.. YEAH.. it rattles.. I heard that Dynamat helps control the rattling ALOT.. but you will stil have alittle bit.
Haven't gotten around to do my.. I don't need that much.. Keon maybe you want to go half and half on a roll.
When I installed my sub, I made sure to dynamat the crap out of the shelf (which does not rattle now).
What DID rattle even with just an 8" DVC and 170 watts was the licence plate, which I matted the rear of and is now all set.
I used Fatmat, which is cheaper stuff. I think I paid $20 shipped for 10 sq. feet. It stuck like the dickens though and really killed the vibes since rear deck mounting will produce a ton of rattles, and I'm 95% rattle free (middle seat belt will rattle sometimes, but it's in the design and no way to fix it). For the price, the FatMat is killer.
(link to pics of my deadening) [url]http://www.chargerforumz.com/showthread.php?t=111314[/URL]