If you are able to put some heat in the AS (like an electric heater) and maybe pay the friend for the power, the exterior of the AS will not become cool enough to have condensation on it inside the building. What is happening now is that the AS is becoming cool to cold and when a warmer day occurs the interior building moisture (which must be high) causes condensation to occur on the cold trailer, until the trailer warms up. At that point, it should self dry due to evaporation. This is sort of like condensation on a cold drink glass. Eventually the ice melts, the glass stops condensing any more water and will even self dry.
But, this cycle can happen over and over during a season of storage. The AS gets cold, the building then rapidly warms (lets say in the sun) the relative humidity increases rapidly (dew point goes up) and condensation occurs on cold things inside the building. By heating the trailer and not allowing the skin to get very cold, it will remain above the dew point of the air in the building and no condensation will happen.
I think it would be difficult to have the trailer ventilated well enough and fast enough to have it warm up naturally faster than the building temp and humidity go up. But, I could be wrong on that. Ventilation may keep it from becoming a cold surface in a warmer, high humidity building, but I am not confident that it would.