Piper, I have the same problem.
For the last four years the heli was kept in a barn , steel clad and concrete floor, we had no trouble with condensation at any time of the year.
This last few months I've kept it in No 3 hangar at Fife airfield and the condensation is almost as bad as you describe .
The only apparent major difference is that the farm barn was used and therefore aired daily allowing airflow through as Marchettiman says .
Don't think EGPJ will let me add some 'ventilation' holes unfortunately!