If you were satisfied with the stock speakers I'd think just about anything should be an upgrade.

I'm kicking around the idea of Tang Band 6.5" subs. I like the idea of having a small box and from the 2 reviews I've actually found they seem to be adequate for an entry-mid level system. For ~$40 it's kind of hard to be dissapointed, plus they are small enough that you don't need a 2000W amp to run them so you can save money on an amp too.

 

Check out the kicker comp-vr and the solo baric L7..... I have a buddy running 200 watts to 2 10" comp vr's and it sounds almost as good as my 1500watt system. . . The comp vr also comes in an 8" sub. . . If you are willing to spend a bit of extra money, look at the solo baric L7. . .these 8" squares put out an unbelievable sound for a small sub....

http://www.kicker.com/06/kicker_home.html

 

I was thinking more like a 6.5" driver to an 8" sub able to be surface mounted in the cargo area. I cant have anything that needs its own enclosure, not even a bazooka tube thing. I would even consider mounting it in the panel that hides the seat gap in the back when its folded down, I can cut the metal easy( plasma cutter on hand) so fabbin some stuff isnt a problem. I appreciate the insight but thats not what im looking for,man.