Custom sub box the po of my old truck had custom made. Fit a 15" in there, sounded better than anything else I've heard. The grey plate on top said "PowerSMOKE" cause he thought it was badass lol. When I get my next OBS, I'm gonna make myself a box like this, it worked great and looked at home there, wasn't really in the way. t wish I had better pics... and I wish I hadn't sold the truck and could take more lol. But here:
Fit even with the sides of the "20" middle seat. No leg room in the middle meant nobody could sit there, but they could sit behind the driver and passenger seats just fine.