I live in TN so the vast majority of the time it is simply "cool" in the winter. However, over the next few days it is going to be unisually cold (down to 1F) Since my girls have never experienced real cold or even snow (at all ever), how might I ensure they are safe and warm without using a heat lamp? Their coop is a 6ft tall (9x12) lean-to style shed with the entire front open except for hardware cloth. So it is pretty open, which is great normally, but now I am worried. Thanks for any ideas!