BondingPolycarbonate can be mechanically bonded by standard methods. It can also be cemented by using a solvent such as methylene chloride or adhesives such as epoxy, urethane and silicone. Polycarbonate and also be ultrasonically or vibrationally welded.
Check this out too:
http://www.loctite.com/int_henkel/loctite_us/index.cfm?pageid=325&layout=2
As for mountiong the sub, a polished aluminum ring, same diameter as the speaker of course, about a 1/4 inch thick with holes threaded would be real nice. The ring would spread the load around the entire speaker. I wish I had a bunch of the 1" poly myself, now that I think about it. Good luck:crazy:
With the right stuff and know-how the seams of the box could be pretty dam much invisible. It would be one hell of a project though. I would practice on some small scrap peices first, because I'm sure it will take a few swings before you hit a homer.