JL Audio 10WX-4 - this is mounted in a custom 3/4 MDF box that I made. This was my first sub build and I put in a lot of time into building it to make it as solid as possible including liquid nails, deck screws, etc. This isn't JL's top of the line sub, but I think it does a great job of providing a complete sound to the whole system. It fits very snuggly behind the rear dirvers side seat (behind the back seat in the storage area) with pretty much no room to spare. I was very pleased with how it turned out. I have a few pictures of it under construction if you'd like to see.
I'd like to get $150 for it. I know shipping may be a bit, but I'm willing to work with the buyer so it an equitable deal and fair for both parties.
Please let me know if you have any questions.