I have a camper coop, and i have set up a double roost by the back bay window area. At the top, up by the roof there are little crank windows that provide ventilation and keep the humidity down. I also put down deep bedding at the beginning of winter. I don't use heat, but the windows allow themselves to sun themselves, and the double perch system lets them pass each other without anyone having to jump down. It was very cozy during the day! An added bonus of the deep litter was that i could toss corn in there and they would dig around all day, which helped with the winter boredom.
Most of my girls are EE's, and don't lay during the winter, but i had one orpington and she layed an egg nearly every day with no added light or heat! The only downside to the bay windows is the need for them to be shaded during the summer, but an awning would do the trick if you don't have trees like i do.
This is as far as they went when it snowed! I threw a few out there but they liked their cozy digs better!