Extreme cold lesson learned by me on this trip:
UQ suspension (aka shock cord) will lose its stretchiness in extreme cold and doesn't snug up as well. In the wee hours of the morning, I started getting a bit of CBS as the suspension stretched out but was too stiff and cold to keep tension on my UQs The solution is to readjust/tighten, but I didn't fully realize what was going on in my half-awake state. It never got really bad, just not as warm as when I first got into the hammock.
FWIW, I had a zero degree full-length Hammock Gear UQ, with a 20 degree 3/4 length Hammock Gear on top (outside) of that. The extra length of the shock cord suspension for the 3/4 length was the culprit behind my slight CBS! I had enough insulation, but it needs to be "tight"!