Sounds like you have a good plan. The heat tape has a thermostat control at the top, right?

Something that really helps is to make sure the waterer is very well caulked/gasket/etc to the concrete so no cold air can get in under the waterer.  My  Miraco 3100's came with a rubber gasket but did not seal very well on the broomed surface concrete. After bolting it down I caulked it all the way around with the best roofing cement I could find in a caulk gun tube. That is about the only thing that will stick long term to both concrete and plastic. Let it set up a few days before using. If you don't caulk it when you put it in and everything is clean it is much more difficult later.

Also make sure the access door seals very well. If not caulk it also with some regular cheap window caulk that can be easily removed.

In very cold climates the best appproach when installing a waterer is to use a belt and suspenders. Good luck.

Jim at Dawn