How do I dehumidify a season cabin in the winter
You are correct that dehumidifiers typically do not operate below freezing temperatures.  In fact, many do not operate well if the temperature is below 65F.  Certain high performance units are rated to operate down to temperatures a little above freezing.

If the goal is to suppress mold growth by maintaining indoor relative humidity below 55% during cold temperatures, then the obvious answer is that both a high performance dehumidifier and a heater are needed.  Looking at the psychrometric chart for moist air, 56F air at 55% humidity has a dew point of 38F.  With a high performance dehumidifier and a heater set to maintain an air temperature of at least 56F degrees, the RH of the air in the cabin could be maintained at or below 55%.