I have to 400w jbl 12" double magnets in a bandpass in my trunk and i had rattle to here is what i did. first secure the license plate. what i did was put little pieces of foam adhesive between the plate and the car itself then screwed it in. Next was the trunk rattle. Go to home depot and get a can of spray foam. about $5. Then open the trunk and remove the liner from the actual lid itself. there are about 10-15 little clips. once opened spray the foam all inside the inner working s of the trunk. let it sit for about 20 min. and my rattling totally stopped. also make sure the spare tire is really tightly secured. Hope this helps

 

Hey Juice, I have the exact same setup. Two JBL GT1200's in a bandpass. I already have the foam, I've sprayed a lot of the trunk down with that (it's thin)and I also dynamatted my trunk liner. I planned on doing what you did as well, but one question-do you lose the ability to use the key to open up the trunk. I remember somebody else used the foam and it warped their trunk AND made them not be able to use the key to open the trunk. They could only use the remote or the button inside the car? Lemme know. Thanks

 

If you do, as much as me anyway, AT LEAST disconnect the trunk release in the front seat so thieves can't get in it without the key! And if you really care, change the lock to a heavy duty whopper of a lock.
I've seen trunks pryed open easily with the factory lock. It killed the paint job, but at least the F-in thief didn't get what they came for.