If you have rattling plastic panels in your trunk, especially with a sub in the trunk, you'll want to treat your trunk with two things.
First, Damplifier Pro should go on all the bare metal of the trunk and on the trunk lid. If you have a sub back there, you should cover 100% of the metal;
if not, at least 60% coverage is good.
Next, you'll want to install OverKill Pro closed cell foam between any plastic panels and metal that are rattling together to decouple the surfaces.
If you want to get the most out of your sub and don't want road noise and tire noise muddying up your music, install Luxury Liner Pro MLV + Foam at 100% coverage to block airborne noise.