I have the "hot Box" and for what I paid I can make myself. Its just a box that is covered with factory fabric that any upholster can sew together. My opinions... build the box yourself and get it covered. The fella that put mine together did a crappy job with the mounting holes and I had to rebuild the thing to get it to work. Further more I had to cut it down about an inch because I was getting shoulder pain because it was too high.
I’m not a big fan of Pioneer but they do make a shallow 12in sub that sounds pretty good. I would recommend a shallow mount sub so you can retain a lower, to almost stock height to the armrest.
I have a JL 12 but it is not wired in yet. I’m sure it will sound just fine, the box is within the speces of the sub and I added batting for a tighter sound.
I just made adaptors for 5 1/4 component speakers for the rear doors. I should have an e-mail-able copy of the template I made for distribution here tomorrow... let me know if anyone is interested. <S> BH