That's a good point and something I'll definitely be testing before moving to the system full time. I'm not expecting to see too big of an issue though, the shelves in this unit are ventilated so that should help avoid too much heat building up in the plastic and I wouldn't expect ~200 degrees to melt the shelving.

That said, I'm actually considering combining this with a rheostat I am using right now. Thermostat ---> rheostat ---> flexwatt/heater. This way I could use the rheostat to put a fairly accurate max temp on the flexwatt and the thermostat would maintain the temperature accurately.

I'll at least go this route until I get bored enough and make my own flexwatt controller with a spare arduino chip