I wanted to add some base to my Auto Audio but didn't need to shake the neighbors windows. I used a basic design found here on the RX7 site but decided to experiment a little with the materials.
Using cardboard and saturating it in fiber glass resin inside and out The front baffle is 3 layers and the rest is 2. The inside of the main box was seamed with silicon and just because I had some I coated the inside of the main box with under coating. Around the vent(paper towel tube) I stuffed poly fill.
The speakers is a 6.5 in Dayton, 100 wts rms .
I don't have performance numbers but the seat of the pants test feels good and a plus is it's hidden away back in the tail lights.

 

Nice!