Tigergenesis: I'm used to cycling fishtanks, so having a tank setup but empty for a week or 2 while I'm tweaking it doesn't bother me.
I think what I'll do is get a screen top, and see what my humidity is like with this substrate. I can always modify it later with plastic wrap/duct tape/etc.
You guys/gals have a favorite UTH brand? I know some people use human heating pads, but I'd also seen several posts around about them just keeling over which makes me a bit wary.
So, ditch the CME for two UTHs, on on the hot site and one on the warm side, probably with a red/black/whatever bulb for night time viewing and basking.
Hrm..now I suppose I really should setup a couple cages/tanks in a spare bathroom closet for rat breeding...
--Maarken