Proper volume of enclosure for wetsounds SW-65?

Okay, nobody laugh, but I'm planning to make tower speaker cans (directed inside the cabin, not back to the rider) out of 6 inch pvc pipe for a pair of SW-65's that have been sitting in my basement for ages. Something similar to what this guy did:

http://www.rzrforums.net/projects-ho...r-install.html

Does anyone know about how large to make the enclosure? If I go with a PVC cap, like this guy did, instead of a pipe plus a cap, it'll be easier and probably look better, but I'm not convinced the cap will provide enough volume.

And just FYI, the SW-65's are the ones that take 60 watts apiece.

It's an infinite baffle speaker so placing it in a compact pod will inordinately raise the resonance and reduce the midbass. Ideally for an infinite baffle 6.5" you might want one cubic foot net. You'll never get that. So go as large as you can without the tube being so long that it looks odd.

Thank you!!! I'll post up some pics of the finished project.

Use black HDPE not pvc. It contains 2 percent carbon black in the resin mix so degradation from sun exposure will not be an issue. Pvc fades and also becomes brittle after exposure to the sun.