I made my waterer with a 5 gal bucket and lid, used 4 nipples on the bottom, and added a small fishtank heater inside a large pickle jar that was filled with water, then placed the jar inside the bucket. Heater was only like $8 at Walmart, the jar I just had lying around. And even if water runs low, heater is inside a jar filled with water, so it won't melt the plastic bucket. Had temps down in the single digits, and no problems yet. I'll see if I can get a pic tomorrow.
My original idea for a watering system had aquarium heater(s) in large PVC pipe with nipples, attached to a cooler and a circulating pump. Unfortunately, my experience with aquarium heaters shows them to be somewhat unreliable, and prone to internal leaks. I may revisit the concept using a bird bath heater in the cooler, but at this point it seems overly complicated, since the bucket/heater combo works so well.