Good luck! But keep checking the nipples to make sure they aren't froze up. I've seen many people say that the water on the inside was not frozen due to the heater, or tape, but that the nipples themselves were frozen. I've not seen one with vertical nipples which made it to zero. about 15 degrees is about the lowest i've seen... Maybe someone else will chime in on that, someone who has tried vertical nipples in the winter.This is the "Hen Hydrator" I picked up from Big R. Works great.
This is what I did to winterize it. Sorry for the bad picture. I didn't want to take my glove off in the blizzard, so this is a shot take using my nose on my iPhone.
I bought 12' of electrical heat tape from Home Depot and wrapped it around the hydrator about 5 times. I secured the heat tape using foil duct tape (stiff aluminum foil stuff that is really sticky). I then wrapped the whole hydrator in foil backed fiberglass insulation which is about 2" thick. I covered all the exposed fiberglass with the same foil tape so the chickens wouldn't peck at it.
Despite being covered in snow, 22F outside, and blowing at about 30 mph, the water is not frozen and comes out the nipples at the bottom just fine. This is the first easy going test. If it works when it gets to be 0F outside, I'll declare victory.