I took an empty 5 gallon hydraulic fluid can and cut off the bottom to about 6-7 inches tall. I then mounted a light bulb base onto a piece of plywood and another couple on top of that to raise up the can and to make a recess for the can so it would stay put. Plugged a thermostat plug (on at 35*, off at 45*) into the base wires, put a 25-100 watt (depending on how cold it gets) into the socket. Place the can bottom over the whole thing and top with your favorite waterer. I posted some photos a few weeks ago, they should still be available via my profile link. Otherwise I can send some to you. I am currently using a 25 watt bulb and it seems to be working fine. Not too hot, not much electricity draw, just enough to keep the water from freezing. When we get another emply can at work I will make one more.