We just had a night of hard freeze here in Palm Beach County, at 7 AM it was still 32 degrees and the bird baths were filled with ice. One of my broodies has quit her project, she had discarded 2 eggs the night before & last night she was fussing & pacing around her little cage and the last 2 eggs were cold. I haven't yet had a chance to check them, the first 2 looked like duds.
But the other 2 hens are still on the job. They're each in a little cat carrier, side by side in a little pen. Last night I piled patio chair cushions around & on top of the carriers for insulation, and placed a board against the pen to ward off the wind. The hens are setting almost flat on top of their eggs and haven't moved much today. It will get progressively warmer here in the next few days.