Thank you! I'm pondering doing something with the cold side--probably a hide (he doesn't really use the one under the bricks). The only times he goes over there are when he's active (usually meal time) to stomp on the plants. I'm also thinking about some more non-succulents to raise the humidity. 4 or 5 in a flat to create a little undergrowth for him. He'll probably destroy them eventually, but herbs grow fast & easy, and we have lots in reserve.
He slept under the big rock one night, but never again, and now he's too big to fit.
Added the (mostly) basil forest today with the hope/intent of raising humidity.
(There's also a Sansevieria trifasciata in there, and I forget what's in the front from the spares.)
In the first few hours, humidity hasn't reached 40% yet.
ZaRDoZ hasn't noticed/discovered that, "Something NEW has been added!"
If this (or something similar) works out, I'll cover the outside of the white tray with leftover tiles from the backsplash. If it doesn't work out--or he decides he "doesn't like them", we have others to try...