I was using WinISD to see how many cubic feet would be best for my sub with a sealed box, a Fujitsu-Ten Eclipse SW4200 (12"). It says I need 4.63 ft^3 (8000.2 in^3). But with a rectangular box, I can only get 5520 in^3 where I'm putting my box in my wagon. Should I make one that is the 5530 in^3 (or smaller), or would an odd-shaped box that uses more space work?