I'm a little late to the party but to prevent condensation you need to move the dew point to the outside of the container.
If you insulate the inside the dew point also moves further in, insulate the outside and the dew point will be on the outside of the steel with minimal heating inside.

In a non breathable structure like a shipping container you also need a a way to dehumidify the air if you are going to work in there. That water you see running down the walls was sweated out of your butt crack an hour ago. :(