I figured up your box dimensions and port guessing 0.25 cubes displacement per sub (close enough, i can correct if you're anal about it).
to end up with a 30 hz tuning like you're looking for the port would need to be 26.5 inches long leaving you at 17.528 cubes after all displacements and 14.6 square inches of port per cube.
nothing about that box is wrong per say... but i personally would do it.. and damn sure wouldn't run 1500 watts per Q in that size box. Just be careful with it, you could easily overheat or bottom out a sub in it.