Yes, yes I have, and I will be complete in about 3 days, just got to wire it up, it passed testing today.
Sub used: Amazon.com: 15-SC10D4 - Memphis 10" Shallow 4 Ohm DVC Subwoofer: Automotive
Amp used: JL Audio JX250/1 Amplifiers - Car Audio Amps & Amplifiers
Ill get you some dimensions when i can.
Remember if you build the box, build it strong, We took out struts that support the person who sit in the seat and inserted the sub box there, and made it capable to bear weight (currently four 175lb rated zipties). We had to cut a very large amount of foam away, so the seat probably is not very comfortable, but you may have more room in your jeep (This was a 2006 Jeep Wrangler TJ) The seats seem to vary from jeep to jeep.
Some really bad images:
Use loads of clamps
turn it into an octopus.
and then (bad quality) (underneath of the seat)
This project is using seanomck
's 2006 Wrangler TJ.