Glad to hear I'm not the only one...we insulated due to the summers not the winters. We have zero trees near this new house- just moved here in July. In the height of summer the metal walls of the coop was hot enough to give me a second degree burn when I leaned up against it. Inside it got over 130F WITH ventilation. We installed fiberglass insulation and covered it with plastic panels (shower stall panels) which are super easy to clean. Between that, the ventilation fans and the air-conditioner, it stayed about 80F which was just fine for my ladies, on the hottest days of the year. We don't worry about winters at all here in northern Louisiana
We installed a window unit air-conditioner in addition to the mini- split unit installed in the wall itself. I was happy to learn they have a 'dry' feature that helps reduce humidity in the coop. They also are great for bringing in outside air on 'fan'. Highly recommend. The fancy ones have blue tooth or connect to wifi for even more peace of mind.