I give them hot water in the morning - takes a lot longer to freeze. And if you go out at midday and top it up again with hot water it will probably last until night - depends how cold it is. The bigger your water pot is the longer it will take to freeze.
I set the waterer inside a heated birdbath (with no water in bird bath) and it has worked great. I had the birdbath in storage in the garage and instead of going out and buying a different waterer I thought I would give it a try. It sits in their pen on top of a piece of hard pink foam insulation (wrapped in cloth) and the pen is wrapped with clear poly. Water hasn't frozen yet, but we are having an unusually weird/warm winter.