So here's what I have to work with; it's a 4x2x12 Boaphile enclosure that I bought used. It's got a built-in divider and light fixture, both of which I tore out.
First I'm going to mount the UVB tube under the lip above the door. Here's the original light (black) I removed, and what I'm putting in, a Reptisun 5.0 t5 bulb I plugged into a 24w t5 fixture I bought from a grow shop.
Now the original lamp was stuck up in a little crevasse between the seam of the box and the frame of the divider, and it was way too shallow for my fixture. So I used a utility knife and removed about a 1/4" chunk of the pvc from the corner inside the upper lip of the front door. This thing is incredibly awkward to work with because it's all one piece, and only a foot tall. My boyfriend laughed at me for being wedged up inside it.
I rotated the image so it wasn't so topsy-turvy; the vertical section is the one I had to trim (it's slightly uneven), and the upper section is the same as it was originally.
Using a hand mirror, some duct tape and a sharpie to mark where i'd be drilling, I installed the little clips that hold the fixture in place. In this image, the empty hole is the one on the ceiling of the enclosure, which used to hold the little black light. The bracket is what I've just installed today, one above each door.
Success!
Step two, is the basking spot. I chose the lowest profile ceramic fixture I could find, then used duct tape again to make a guide for where to drill.
Using a mirror again, I fit the mounting screws, then installed the lamp. It's not wired yet. I'm going to drill a slot in the back to run the front end of a wire with a dimmer, which I scavenged off a fixture from a different project. Then I'll wire the thing, re-install it and adjust the light as needed.
(Sorry about the flash reflection here)
Voila.
That's all I've got for right now, I'll put up some more progress pictures as I get the wiring done and put in the bulbs so I can measure temperatures. Any thoughts or suggestions would be appreciated!
Wow! 
I got her enclosure off Craigslist same as I did this one. 4x2x2 with glass sliding doors. I modified that one too, but only by installing another lamp. Woohoo DIY!
