Floors are steel cross beams from side to side with wood decking installed on top of that. I have seen a lot of containers with rough oak deck for floors.
The best way to keep the moisture out is to put louvered vents around the base and top to allow air flow. Temperature differentials will always be in favor of having a dew point inside that is lower than outside and it will sweat. Keeping the air exchange with outside will help keep the dew point equal inside and out keep condensation to a minimum.
