Despite my best efforts, the freezing continued to be a problem.
The first (and likely most important) step in mitigating this problem was to move the waterer away from the windows and doors. This makes filling it a bit more of a pain, but it’s not so bad when you’ve got a new fancy filler thingie. Windows and doors are convenient for filling, but they have a nasty tendency to let a lot of cold air in, especially in a drafty chicken coop.
Then there were the hardware updates:
The body of the waterer assembly all got a nice layer of foam insulation.
Followed by a few layers of duct tape. As I have found out the hard way, chickens will absolutely destroy any unprotected insulation in approximately 2.4 seconds. Any visible insulation is history, so apply duct tape liberally.
Inside the reservoir a few reliability improvements were made as well. The water pump was secured to the hose with an excessive number of zip-ties. The other end of the hose was secured to it’s fitting with a screw. Without all the extra fasteners the whole thing tended to disassemble itself at inopportune times.