As long as there is some opening, then you should be as good as you are going to get. With the temps as they have been this year, I think unless a flockowner has a completely climate controlled coop for their birds, everyone is going to see some amount of frostbite before we are back to warm weather. It actually sounds like a cozy set-up you have if it is a South-open one. I hope they all do well this week. It was 42˚ a few minutes ago when I came back from getting groceries. I am not going to like looking at the thermometer in the morning though. I cleaned a couple of coops and pens myself today while it was nice enough.the whole south end is completely wide open except for the framing for the door and the hardware cloth. The blanket only goes down on windy days, especially when coming from the south. There is at least a 6 inch gap between the blanket and the wall of hardware cloth so there is a ton of air movement around the blanket and even through it. The blanket just lessens the wind thus reducing the drafts inside.