Could you remove the edge board they try to perch on and replace it with a strip of thinner wood? Something like a board or another material maybe 1/2" thick, something that would be too thin for them to be comfortable perching on? Plexiglass would be really thin, but it gets expensive.
My solution for a homemade waterer. A plastic Pure Leaf tea bottle filled with water. It was out there from July to just now without them trying to roost on it. A gallon milk jug of water would be bigger and weigh 8 lbs so would be difficult to knock off.
I do the same...heated dog water bowl. I sometimes put a piece of board over part of it so the whole top is not exposed to whatever might get scratched into it.
Couple ideas. A standalone power station like a Bluetti (there are others) that you can take in and out of the coop, maybe even daily, and charge it in bad weather situations. Could you elevate your extension cord on a pole high enough to get out of the path of plowing? Worse case, and I have...
It is my understanding that the electrical option will not have battery back up. You have to use one or the other. I have an Ador mounted inside the coop. It's great! The accessories - external push button and external light sensor are easy to install if you need any of those options.
How about a smaller livestock tank with an electric heater as suggested above, or a heated tub? Those electric tank heaters can heat up quite a few gallons. Check TSC. You would have to insulate the outside and cover part of the top leaving just enough of an opening for them to access the...
I have bantams and a new coop in which I installed an Ador automatic door to the run. Best thing ever. I don't have to go out and shut them in or worry about not being home.
Also I have a Rent a Coop treadle feeder which is inside the 10x8 coop. I attached a rubber mat to the treadle and set...
This chick is about 9 weeks old. It was an extra put in an order of bantams and it's a full size chick. I don't know what it is or if it is a hen or rooster. It came with a broken foot but otherwise has thrived.