I have an '05 X2 (now X1) with the factory JL free air sub. I like the location of the factory sub, but I do not like the fact that it is a free air sub. Do you think it would be possible to build a sealed box behind the sub mounting location and replace the factory sub with a JL 10W7 (or other higher end sub)? -- I would throw more power at it of course (e.g. JL 1000.1 or the like) I want to keep things as close to factory looking as possible.