OK - in my search for the optimum sub location, I came across this image that seems to fit in some 'dead space' between the seats. I think Dodge Vipers have a similar set-up.
It looks like they are using a full size 8" sub with this custom enclosure which includes extra space on top of the engine for an even bigger cavity.
Not sure how it would sound with a sub right beside your ear, but I thought the concept was really cool. With a slim-profile sub, could likely even make this a stick out little less (although I hear you Patrick on the questionable sound quality).
