Even if you are pumping, I wouldn't rely on that alone to keep it from freezing unless you have some heat in it too for those coldest days and nights. My coop is 10-15 degrees warmer than outside, but that still means when it is -20, it is -10 inside. Even wrapping in poly might not keep it warm enough? I would make sure I had a back-up plan just in case.
I use large heated dog bowls, but they have to be cleaned daily which is a pain in the butt. I am going to try some nipple waterers with a 2.5 gallon bucket inside a 5 gallon bucket, wrapped in heat tape and insulated in between. We shall see how that holds up. I will still have something underneath to catch if there any leaks or drips. I may try a second method using a 3" PVC pipe wrapped with heat tape and insulation too. No way to test different ways until the cold hits, so I need to prep those on these rainy days.