I'm getting a box design for my HT subwoofer, and I need a hand.

I'm a car audio person, and usually only deal with frequencies down to about 33 or 34 hertz. However this enclosure will be tuned to 17.7 hertz.

Some information about it..

amplfier will be a Dayton HPSA1000 (1000 watts RMS at 4 ohms)

subwoofer will be a RE Audio SX18 (dual 2 ohm rated for 1000 watts RMS)

enclosure: 60" tall, 24" wide, 24" deep.

17.14 cubic feet total

8.74 cubic feet after displacements

tuned to 17.7 hertz

Now, I have already figured out the bracing. They will be "squares" that have 2.5" rails (not sure what to call them) and go around the box, exept for the one that is next to the woofer (see pictures). I'm debating whether or not to double up all 6 sides of the enclosure to make it more rigid.

suggestions?