One of the advantages of a free-air (or infinite baffle) installation like mine is there is no MDF box to be found. The sound is very linear as long as you seel the trunk ("boot"). And it's quite stealthy/clean as well. The way it's done is the back panel of the trunk is removed, and rebuilt in MDF, the MDF is then cut and speakers and installed in them, the edges of the MDF mount is made to create a seal, re-install and voila. :) Nice clean bass in the cabin even with the top down. :-)

I'm using JL Audio IB subwoofers. They're intended for just this purpose.

I'm using a Phoenix Gold amp, and the amp has a remote attenuation knob that's mounted in a secret location I can reach with my hand, so then I can adjust the bass for top up and top down and highway vs street with a little twist. :) :)

The best part is I retain my trunk, I can throw a full suitcase in there now. When I had a 8" bazooka tube, I couldn't fit anything in there except the tube. Plus the tube tended to mush out and create bass that doesn't exist. I've quite happy with the built and quality. I've had a lot of bad experiences with audio installation, (you can check by searching the site ;-) so if i'm happy with the sound on the first go, then that says a lot :-).

Calvin