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.
They got the leftover lasagna all for themselves. Even my pig of a cockerel was happy. There was so much the bigger hens didn't bother chasing him off. His normal MO is to dart in, grab the biggest beakful he possibly can and then dart away. This time he just took two steps back, wolfed what he had grabbed and stepped back for more. 
Everyone is happy. 
