plexiglass

Does any body know if a snake under the tank heater could potentially begin to melt plexiglass?

I think the melting point for plexiglass is 140-160 degrees C, somewhere in that range. I've heard of UTHs getting up to 110 degrees, but never that high. I wouldn't say that it couldn't happen though. Overall, I wouldn't think of it as too much of a concern if you have a decent UTH, you keep an eye on it with a thermostat and thermometer, and provide proper air flow.

A Corn's safe maximum is 90 - anything over that could harm or kill it (in extreme circumstances), so you'll always be keeping your UTH below that temperature with a dimmer or thermostat. So no, in that situation a UTH will never get hot enough to melt plexiglass.

If it got hot enough to melt plexiglass, your Corn would be deceased a long time before that happened.

One thing I'd say is that I've had a viv with plexiglass doors, and they can get scratched and go cloudy over time from normal day-to-day use. Whilst being more flexible and easier to shape and handle than glass, the surface of plexiglass is much more fragile and easily damaged.