It looks like a 3 cubic foot box tuned to 20 hz would work pretty well. It would require a 4inch port 20 inches long. Being in a dorm or apartment may help things out for you. You could build a long enclosure 1' x 1' x 3' and fit that port with no problem. Maybe even make it thin enough to fit behind a couch or under a bed. A little vibrating under the bed may convince the girlfriend that it's a good idea!
