Professionally made subwoofer enclosure for an MK3 jetta. A pic can be seen here
The pic doesn't show it really well, but it leaves plenty of space for whatever the hell you might want to fit in your car. In fact a friend of mine has actually crawled into the trunk and closed the lid with the enclosure in place.

It is designed for a 12 inch woofer. 2.4 cubic feet. ported tuned to 33hz. Sounded really great with my HE2, but now it's sold and the enclosure is up for grabs. Basically make some offers people. I don't want a lot of money for it so you can lowball all you want and you'll probably get it. Just can't keep it in the house forever. Anyway to buy the materials or a prefab box will probably cost you more then to buy mine.

Contact if there's any degree of interest. I'm sure we could work it out.