[mikegett]

A few suggestions. The tape is ok, but will be difficult to remove from the finished product. I prefer plastic. The large sheets at the hardware store work great. What ever you do chose, use a release agent. Spam seems to work pretty good. The problem with the tape is that the resin tends to drain between pieces. Now comes the important part. Just like any box, the volume is critical for the performance of the woofer. Once you have determined the volume, you will want to incorporate it into the new design. The easiest method is to find something that can be measured and then shaped. Some of the stores like Hobby Lobby carry foam beads. They have a slight moist texture and stick to one another but hold the shape you mold them to. Just measure out the volume using a pitcher and then shape it in your car. The trick is to shape your volume and then do the outer layer first. This enables you to scoop out the foam, plaster, or what ever you used. Then you can do the bottom layer. The third step would be to join the two pieces and thicken the final product. Good luck and let us know how it goes.