I actually have seen a pre-fab subwoofer box for 10 and 15 inch subwoofers which fit into the spare tire well on most coupe type vehicles. If you are still looking, let me know and I will try to find the contact information for the installer I last used whom I know has these units. They are in Boston, MA, USA. I can't seem to find their info on the web and need to get my reciept from them for the phone number.

Greg