1. The reason not to use Amsteel or similar is shock load - no stretch to ease you in a fall.
2. I wonder about tunnel vents near the top of the sock. Bibler used plastic tubing to make a stiffener on some of his tents to get an overhang so the top of the door could be left open to vent. I wonder if you could do a version of a tunnel vent near the top. A couple of them with a way to close them off on the weather side could set up an air current in the sock to give you a small breeze rather than trapping hot air from your body heat. Something to ponder about after the basic sock is tried.