Containers are awesome storage but you need to add some ventilation to them, those tiny vents are good at stopping 40' waves at sea but don't breath enough for storage, a little water gets in and it's in there forever. Torch or cut in a couple of 1-2 square foot vents near the bottom on one end and near the top at the other before you put anything in and it's all good. A little bit of metal flashing along the top edge over the doors shields the seals from leaking too.