In my opinion, you're going to have a tough time hanging a ported enclosure from the rear deck, much less 2 seperate. I see the weight of the box(es) being an issue, and possibly space being another.
Have any pics of the rear deck area that you're thinking about using?
edit: Looked through your pics and saw the idea you have but no pics of the actual area involved. Are you going to have the box "hanging" from the rear deck, or going from the bottom of the deck to the trunk floor?
Also, I saw it mentioned that this was a "t-line"? The drawing looks like a ported box with lots of bends to accommodate the needed port length, not a t-line as I understand one to be.