Plans can also be purchased there. There is a ton of information regarding their construction on the site's forum. Bill knows his stuff.
I apologize in advance for the crappy camera work. I really wanted to get this box in action on film as quickly as possible. The camera mic distortion when close-up masks just how articulate the box is under power. At "War Volume" the car is unbearable to sit in as it's just too loud for my ears, but the meter doesn't lie about the box's efficiency. It can take another 6 volts or so before power compression sets in. All that from an 8" driver consuming ~20 watts. There are no stiffening caps, anchor-line sized power cables, improved alternators, or outrageously priced components.
This system: -BFM Auto Tuba built to spec -Class D amp -Stock CD player -Bass blockers on the mains