OP: I know exactly what you want. There are appropriate pre-fab sub boxes available. You should add in some braces(this is not hard; just buy a cheap mitre box with manual saw and buy some 1" x 4" oak boards from your local Lowe's or Home Depot. Please refer to bottom of this post for details on bracing. What about this cabinet? http://www.deepsurplus.com/Speaker-Parts-Amplifier-Building-DIY-Audio/Empty-Sub-Woofer-Cabinets-For-DIY-Speaker-Building
