Check it out, now that's a nice set up. I read though that some of them don't line up correctly. With the couple you've done, did you run into this problem?
The first one I did run into a problem with fitment. JL auctally put production on hold till they got the problem solved. I spent a few hours on the phone with the guy who designed the box. Changes were made and the ones I've done since then have been fine. It's like anything though you have slight diferences from the factory in the truck and with the box.
At the shop i work at we've actully done a couple of setup's with 12's a 15's thru the midgate and building a fake wall to replace the midgate.. havn't had any problems with leaking or anything...