When I've built sub boxes about that size, I've used 3/4" MDF, internal bracing and doubled up the baffle holding the driver. I'm not sure the last was acoustically necessary, assuming lots of bracing. It was more that, if the driver is inset into the baffle (which it was), you wind up having the driver screwed to not much MDF behind it unless you double up.

It's hard enough moving the #$%^$ things with one side doubled up. I can't imagine doubling up all six sides. Nor have I ever used MDF stock thicker than 3/4".

e

• Tempest Construction Pix