Well i think i figured it out. It'll be 5 cubes after the bracing, driver displacement and port displacement. The port will be 4" x 13.5 and it'll be 22 inches deep. So thats 53" of port area. I was told 10-15 per foot of internal volume so that works. And each sub will have 2.5 cubes. I think i'm ready to get plywood!