hey AB..
looking at your drawing, i think that corner loading would greatly benefit from the rear vents, like in the jensen cab... using your corner walls as part of the system. of course timing the front and back waves is important. as far as crossovers go..go active . im using ashly gear, a stereo 4-way with adjustable sloping. i like it for the simple fact that i can cut out of my subs as low as 40 hz.