I have made 2 sub enclosures out of PVC pipe in my 87 Mustang. I have installed a rear seat delete kit but still wanted to hide my 2 8 inch subs. The idea was to hide the subs behind the front seats near the floor facing the front seats. You can see how it came out here...
https://drive.google.com/file/d/0B8t...U3c/view?pli=1
The sound is incredible and the cost to do this was low since I used 3/4 MDF for a cap.