Ask your local hardware about setting up a heat lamp on a thermostat. It is not very expensive to do and would prevent overheating or freezing, especially if the temperature changes significantly while you are away.
Our girls are free range too, so if it is Marek's it is all over my entire property. We are due for snow and Saranac Lake is repeatedly the cold spot of the nation. Will the freezing temps kill off the remaining contagion? I can deal with the coop, it is the great outdoors that I find daunting.