Well, after four weeks of only being able to work on it 20-30 minutes at a time, I finally finished an 8" sub enclosure for the tool cubby in the back passenger side of an x-cab. I used 0.5" MDF and the enclosure volume is just a hair over 0.2 cubic feet without a speaker. I don't think you could make it significantly bigger without cutting sheet metal. I prefer the sound of a ported enclosure so I added a 1.875" dia. x 2" long port, but at this small size a sealed box would sound pretty good too. The sound quaility is pretty good for the size. Much better than a simple mounting plate over the cubby hole. I was able to back the gain on my amp down by about 2/3 and still get much better response than a free-air setup. It feels like a three year old is kicking the back of the seat. My total cost for materials was only about $25, and I have enough left over to make 3 or 4 more. I have pictures, but if I make them small enough to post, you can't see anything. If someone would offer to host them that would be great, or I can e-mail them to anyone who wants them. Next weekend I'll have to remove it to make some minor adjustments and I'll measure it all out and make detailed schematics for those that may be interested.