Need some advice on designing a new enclosure.

[DeeBoy718]

Well, if you're removing the box to deaden, I would go ape shit and double-layer wherever you get the most rattling, the trunk door, the metal directly facing the enclosure for example. A simple way to check how much deadening you'll need to do is to pull all the trunk panels and knock on different areas in the trunk. You'll notice that in some areas, the metal will sound more "tinny" than in other areas. I would double up where the metal sounds the thinnest, and single layer everywhere else. I would try and do the entire trunk one time so that you don't have to go through all the work of having to remove everything more than once.