I haven't used other software, but if you are serious about building your own subwoofers, Bass Box Pro is really the best. You don't have to buy anything. It's up to you if you are really picky about how a sub performs.
You could just buy a SanSpeak or Morel subwoofer. Then do dynamat damping on the interior walls, and then spray-glue some Acousta-Stuf Polyfill on the inside walls. Like timlub said, the stuffing will damping some of the peak that happens right before frequency roll-off. This might help work with some of these other subwoofer drivers.