We use a CHE above tubs currently for 2 baby kingsnakes, no hole in the lids, it has about 6 inches in between the lid and the CHE. Probe is right under the lid. Never had an issue. No melting tubs, no burned snakes, they are doing very good! It's also temporary, we had it set up a few weeks in advance just to test and make sure.

We considered cutting a hole for the lamp and putting some netting to make sure the snakes couldn't escape but it wasn't necessary really.

We tried UTH, it is catching dust now. Honestly personally the worst kind of heating I've tried. It simply doesn't get through the substrate, doesn't create any ambient temperatures and a snake in the wild would burrow to get away from heat, not the other way around.