I actually put the thermostat on last night. No cracked glass that I could see this morning. Now that I have two UTH's on the tank, I'm not seeing much difference between the two sides of the tanks, so I'm going back to the Home Depot to get a lamp dimmer to put inline on the "cooler" side, to provide enough of a temperature gradient. I tried unplugging one side, but that side was dropping into the 70's, while the other side was in the 90's.
The ambient temps look pretty good, getting into the upper 70's, humidity is around 56%. Just need to get the cool side cooler now.
Thanks for the advice all.