If you are storing any items in a standard shipping container that is placed outside and exposed to the common European elements, you are susceptible to condensation occurring inside the container, which will more often than not collect on the ceiling.
A standard shipping container is just a metal box which is quickly affected by ambient temperature changes. Shipping container condensation occurs when the walls of a container become cooler than the dew point of the air found inside the container. When the air inside a container is not able to contain its moisture, it reaches it dew point. If this occurs, the moisture will change its state to liquid form, building up on the roof and walls, putting in danger your cargo and the interior of the container.