The air space that you need varies for the type of sub that you get. For instance put an infinity DVC 12 in a 1.25 cubic ft. box and then put a alpine type r 12 in the same box and tell me which one sounds better, the infinity will because the r needs more air. You could do it, it would be easier to get the most air space out of your trunk/hatch by doing a fiberglass enclosure but its going to have to be several several layers thick. If you are looking for good clean loud bass get a type r and a box that would match, at least 1.5 cubic ft., and a nice size amp with 4 gauge wiring kit. If you want to have a show set up then start reading on how to fiberglass. Its really not that hard, just takes a lot of patience to perfect it.