Thanks @PirateGirl ! I was thinking of running the extension cord inside the coop through one of the vent openings, then doing a drip loop inside to protect it from dripping moisture and attaching it to the wall away from the vents. I like those covers though, I can add one as well, just in case. I want to keep the waterer inside the coop though, for the inevitable days when the chickens can't or don't want to go outside. I want them to have access to water at all times. This waterer is fully closed on all sides and has horizontal nipples, so it shouldn't evaporate a lot of water into the air.
I really like the solar light/lantern idea! I'll definitely look into that.
Hmm... From what I understand, nipples are prone to freezing in winter... I'm not sure that can be avoided, you can probably keep the main container from freezing, but not sure about the actual nipples.
Also IMHO there's rarely if ever a day they "can't" go outside. I live in a pretty harsh environment with winter most of the year, and the chickens almost always go out for at least part of the day. The only times they stay in are 70mph wind days with ground blizzard conditions, in which case I modify things for them until the storm passes. If it's below zero and not windy, they will head out on their own. If it's snowing, they will head out on their own eventually (though they prefer if I clear a path). But that is your call. I like to leave the door open and give them the option of going out 365.