Well, what's your budget looking like? That will be the primary deciding factor on what we recommend. Also, there are MANY options available for running a sub that will take up almost no room. A sealed 8" sub on 300 or so watts will actually fill in a lot, and require an incredibly small enclosure.

Off Topic: Keith, what is it you have? a 4th order ported through the ski-pass? Or perhaps a 6th order?