Condensation can occur when storing in containers especially during the colder months of the year. The cause can be from one of several reasons such as:
Used containers can have damp floors; The items you are storing may be damp (even mattresses have a moisture content) or some items may be carrying water such as Dishwashers, Clothes washing machines. All of these on a sunny day, even in mid-winter, will turn that moisture to vapour and as the temperature drops that vapour will become water droplets that accumulates on the ceiling and start dripping. To help prevent this use 'Absorpoles' see www.absobopak.com - these are very good at removing the damp vapour from the contained atmosphere, but if you leave the doors open on a damp or wet day the 'Absorpole ' will be working overtime and its life span (on average 3 months) will be down to a few weeks ... However, they really do work! Costs from around £15.00 each and can be ordered for overnight delivery from supplier.
Another alternative is applying 'Grafo' to the ceiling. This is a product developed by British Steel to apply to roof sheets such as aircraft hangers to prevent condensation dripping from ceilings and corroding purlins and fixings. It is applied by spray to ceiling and dries rather like Artex and is very dry. When water droplets normally form this substance absorbs them and when the temperature changes it releases the vapour back into the atmosphere. It's not like a sponge and it doesn’t fill up.
See Grafo Products - Costs £120.00 for a 20' container ceiling from your container supplier.