So I can finally report success at keeping my water from freezing. My water starts at a hose bib in the outside wall of my house, which turns to CPVC, and runs 10' to a Miller King Size automatic Font. I use a 20' long eaves heater wire, the kind that normally goes on the edge of your roof, wrapped around the pipe. At the end, under the bowl, I have that wire coiled tightly and glued to the bottom of the font. Miller would not advise that, but it has not melted the plastic font. The wire starts at the bib itself right at the wall tight against the vinyl siding, again, no melting. This is then all covered in that foam pipe wrap, and that is then covered with a piece of aluminum to stop the chickens from pecking at the foam.
I've discovered the system frozen because my GFI breaker blew, and then 2 hours later in sub-zero weather its defrosted and free flowing again. My only problem with this font is that the chickens often fill it with the wood chips from the floor, so I am doing a reno and moving the chips away and putting a patio stone under the font instead. As far as cost, I have been running that wire, plus 2 x 250 IR lights constantly for a month, and my added electricity is ~$12. Tomorrow I am picking up some Farm Innovations Thermocubes. These are thermostatically controlled outlets that come on at 35F and go off at 45F. Won't make much different in winter, but they will save money now and in the spring.
FWIW, I wouldn't use CPVC again, its rigidity can be problematic, and the joints can't just be unscrewed, I'd go with some form of flexible hosing, like hot water pex. I had a hen decide that the heat from the coil under the bowl was just what she wanted, so she bowled out a spot beside the bowl to roost...;-]