Look into resonant engineering(reaudio) RE 8" subwoofers
They take very little to make them move sufficiently and are amazing woofers. They are rated at 175wrms so the amp needed to push them will not have to be large(size wise or wattage wise) I have 1 right now in a .75 cubic foot box ported to 32 hz and it bangs. It is louder than my 2 infinity 10s were and cleaner sounding on top of that with the same wattage.
Neccesary size for the box is .25 cubic foot sealed or .5 cubic foot ported. Thats a tiny box. You can fit it about anywhere you want. mounting depth of roughly 4" they are very easy to place just about anywhere youd want it.
Because the driver is not very beefy you can also get away with using 5/8" wood without a problem.
Id put pictures up but not all my ftp files were brought back up...