The subs I'm looking at (Polk Momo MM2084) require only 0.35 cubic ft of space each in a sealed enclosure, so I'm thinking about installing the pair in the rear wheel wheels - one on the left, one on the right.

Thanks for your input!!!

I've seen the JL Audio Stealthboxes posted in a few peoples B5 series cars. Holds a pair of 8's. I'm considering them myself for when I get around to ripping out the POS Bose AMP/Speakers and possibly the HU in my 2001.5 S4.

http://www.jlaudio.com/stealthbox/a4.html

and your enclosure on that side would take up less than half the room. Hell, if you got creative, you might even be able to mount both of the 8s on that side and still maintain the little storage bin on the other side.

the ID 8 v2 models. they are very inexpensive and sound awsome. You shouldnt hafve a problem fiting them in there. Mine have the same sealed spec (.3 cubic feet) and take up so little room.