There are electrically heated dog water bowls. Would require only a drop cord and would need to be in coop out of wind and off of ground. Might set it on two bricks side-by-side?
I took large pan of very warm sugar-water to the chooks this am and they really went after it, leaving the other two pans that I had just de-iced and filled up. They downed 3/4's of it in under an hour and ignored the other two with the cold water.
Not a bad hardship to do it twice a day. You are going to do more egg checks than that anyway in these temps, so you will be going to the coop anyway.

Not a bad hardship to do it twice a day. You are going to do more egg checks than that anyway in these temps, so you will be going to the coop anyway.
