i have found a solution that works great for me, i use a 60 watt automotive battery tray heating pad that i put between a couple of ceramic floor tiles. this works for both plastic or metal waterers that sit flat on tiles. i live in anchorage alaska and last couple of weeks it has been -15 degrees. have not had water freeze yet. most durable thing i have found for extreme weather
That's interesting. Where do you get those and about how much are they?
Thanks