can you post up pictures of what the rear part of your rig looks like.
so we can get an idea of your floor space / window location / roof obstructions,,,, ext...
the eaziest way to build a wall in ur car, will to be to make a box that will fit in the rear of the viechle , ( just barely small enough to fit thru tho ) and then make additional trim pannels to attach to the front side of it, that are completely cut to fit the exact shape of your car that will "seal off" everything rear wards. that way if you need to remove it from your viechle - you just remove the trim pannels and pull the box back out.
most walls I have seen have the port across the top by the roof, and the subs under that.