I rigged up a gauge heater with two low watt bulbs on a thermostat, with insulation tape around the interior of the outer wall of the bucket. But they don't quite do the job as well as I wanted. They just can't get the top of the qauge (where the snow tends to collect if there's even a small amount of wind. I'm thinking of using this stuff
http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=13997 instead, wound around the interior of the inner wall of the bucket, and leave one of the bulbs to keep the tipping pans ice free. Since this heat cable is made to be placed in with the reptiles, I'm thinking it should be safer than plumbing heat tape in regards to melting the bucket. I haven't hunted up the lowest price yet, so not sure of actual cost. This place has it for $9
http://www.petmountain.com/show_product/507320/?utm_source=froogle&utm_medium=datafeed&utm_term=507320 . The only worry I have is that it is 15 watts distributed over 11.5 feet of cable (although one site said 6.5 feet of that is "cold" lead cable), so it may not be quite enough heat. But at least I can get the heat right to the bucket wall surface, and get it distributed over the inner wall better, even up to the top.
Steve