We get many nights in single digits (F) and a few below zero. Walls, floors and ceiling are insulated, but nest boxes are just 3/4 in. plywood. They are on the east side of the coop. I'm concerned the hens won't like the cold boxes and the eggs might freeze before I get to them. I don't think the nest boxes are large enough to insulate from the inside (other than the straw filling). How might I insulate the outside? If I were to glue on styrofoam type insulation, would it deteriorate quickly in the elements?