I went throught the same dilemma last year. I ended up keeping a sub in each compartment and went from 2 10" L-5's to 2 12" JL W6's.
Same amp but doubled the volume and low end. It pounds hard. When I turn it up, anything in any of the cupholders starts spinning and dancing around.
The only thing is I want to do now is figure out how to vent the area behind the observers seat.

I went with birch ply, and am really happy with the perfomance of the boxes.