I use those rubber pans too. Mostly in the summer because the hens like to stand in them when it's hot. But they do make changing out icy water a lot easier in the winter if you have to go that route. I do have power to my barn and sheds though, so I guess I'm a little spoiled.
I have two different heated waterers... one is a simple heated bowl. The other is an actual chicken waterer with a built in heating element in the bottom. I HATE it. It doesn't have a cord, it has a spot in the base where it plugs directly into an extension cord... which means the prongs stick out from the base. It has to be filled in an inverted position and it's next to impossible to turn that stupid thing over without sloshing water all over. I don't know who designed it, but they didn't think very hard about the design. When I bought it, it was the only type available and I was in a pinch. I've regretted wasting the money ever since.
I used to change out my stalled horses' water buckets every day in the winter when they froze up by dropping the whole frozen bucket into a heated stock tank. I'd feed and clean stalls and the giant ice cubes would slide right out of the buckets by the time I got done. Then I'd dip out fresh water and be done. The bucket sized ice cubes would melt in the tank so I didn't waste the water! I imagine one could do the same thing with the chicken water, if you're concerned about wasting all that frozen water... and if you happen to have other livestock with a stock tank handy. LOL
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