Gotta say, that enclosure looks very nice and this thread is super helpful!
There's a very good chance I'll be buying/building Kuzco an enclosure of this size (or a 6'x3'x3') when the time comes and outfitting it with halogen lights like you are. I've done a decent bit of reading into the different types of infrared radiation provided different heating elements lately, and it looks like good ol' fashioned tungsten/halogen lights are the only elements that provide good amounts of the IR-A radiation that really gets deep into muscle tissue. I'm interested in seeing what your thermal gradient looks like with the amount of internally-mounted halogen lights you have there. Good luck getting that enclosure finished up, and keep us posted!