I think your res. idea is great. The cap, quartz liner, and active parts from this UV-5 could easily be adapted to your idea. The bulb measures:
I am pretty sure that PVC gets brittle in natural sunlight b/c of the UV it (sunlight) contains -we'll have to check into that.
The bulb is a compact fluorescent, I believe, and contains Mercury Vapor. It is a Hot Cathode type. Here is some more info:
Philips Part No. 046677-38186-3
Desc.
Philips TUV PL-S 5
Watts: 5
UV-C Watts: .18

(That is what is on their web site) Althornin......
Nominal Bulb length: 4 in.
Useful Life Hours: 8000 --> Useful Life Listed @ 85% UV Maintenance
Philips Figure No. 16-S
The quartz tube is flanged at the top and is held in by the lid. I can give you dimensions on any of the parts. I plan to post them, or a link to them, soon. Let me know of any specifics you need.