I read about it, tried it and didn't get good results so I thought I'd report back. Here's the setup. I used a piece of heavy flashing behind the thermostat, thinking it would provide mass and make the water heater thermostat work better. The first problem is that the metal gets hotter faster than the rest of the bator, and the thermostat clicks off early. Hence, it takes a while for temperatures to stabilize at first. The second problem is that when you open the bator, the air temperature drops fast but the metal stays warm. So when you close the bator, the heat doesn't come on because the metal is still warm. Not sure how much of a problem this is for eggs, but I didn't like this effect very well. Anyway, I didn't think that putting the thermometer onto metal really helped the bator with thermal stability. I do think I will try to add heat containing mass to my bator by putting a couple of those hot/cold gel packs in the bottom of it, wrapped in ziplocks. I ended up removing the metal off the wall and bending it to make a heat shield for the light. Now the light doesn't shine right at the thermostat. ps. I'm still tinkering with my bator, so it's not finished. It needs different sized mesh and a shield to keep the chicks away from the light bulb.