Re: lets talk about shipping or sea containers
Pier and beam foundation works well.
Railroad ties on a thick gravel bed [with sand base]
A concrete slab works well.
Convection vents, 2" pvc pipe, one[or two] on each end,
at opposite heights. One end, near the floor, the other end
near the ceiling.
Any venting, etc., I suggest to be done on the sides, as opposed to
in the roof.......it is much easier to keep from leaking.