I have kept helicopters in various types of agricultural buildings for many years. Generally I have found a livestock barn with slatted wooden sides, concrete floor and a complete roof to be the best for my situation. It needs to be large enough that the helicopter doesn't get covered in blowing snow, but it allows the wind and air to circulate around the machine and therefore I very rarely find a problem with condensation. The worst case for me was when I kept it in a corn shed with roller shutter doors, it would often get covered in condensation just when I wheeled it out to fly it in the winter. Though not really a big deal as they are designed to get wet in the rain, and they soon dry off!
I can wheel a wet helicopter back in to the shed with the slatted sides and it will dry off fairly quickly with the circulating air.
Now stopping the horses giving it a rub, thats a different matter......
