building false floor box, need air space requirements for sub Options

[Cormudgen]

I am about to undergo building a custom false floor box for my 6th gen hatchback. The sub I am using is a 12" JL w0. I currently have the sub in a factory box it came with from JL. What i would like to do is build a false floor where the actual box is submerged in the spare wheel well. It is about 4" deep. If i could submerge it 4" in the well and only have to build the false floor 2" up I wouldnt lose that much space. That would be ideal cause then I could use 2"x4" to support the false floor and not have to do nearly as much cutting. What I'm wanting to know is how much air space this sub needs and where I can find the info. Also, when building the box part, after screwing in the pieces together should I use some type of caulk as well? and do I need to carpet the whole box, currently I'm only planning on carpeting the whole false floor. When i do this I fully intend to take pics of the whole install procces so maybe I can write up a tutorial for you.

thanks
cormudgen