Andrew. Two seperate issues. Mail the Swedish clubs that winch all winter long (or special occasions) off the frozen lakes. We started winching 14 yrs ago at 3000 ft MSL, wintertime AV 30F to minus 5F. Issues were cold starts and ice on the runway.

Glass glider issues same as high alt flights. Even when we removed snow and ice, moisture in sploiler boxes sometomed froze spoilers at altitude. In the pattern you find out those wont open and no wheel brake, just before you land in am icy runway. NOT FUN.

There are a pleathera of sources, especially from manf regarding sub zero temps and gelcoat. Polyurethane seems to contract & expand better. Remember Walt Rogers Twin Grob after Bob Harrison went to FL390. Finish looked like spiderwebs