It's been a while since I ran the numbers, but my 24" CV driver is in a 24 cubic foot enclosure (4' tall x 3' wide x 2' deep). The enclosure seems huge, until you put the driver in it, then it seems small. This is with 2 6"x15" ports.
I used Baltic birch plywood, and it sounds fine. I have yet to open it up and add the damping material.
bs