I've got 3 shipping containers I use for extra storage (note; when building your next shop, make it twice as big as you think you will need!). The one thing with containers that I have a problem with is they can sweat. Only one of mine sweats, and it literally rains inside there :violent1: The other two are under / behind the shadow of my shop, and they don't sweat at all, ever. But when it's cold overnight, then the sun comes out the next morning, that's when the one in the sun 'rains' inside. If you insulated them they probably won't do that.
The house / shelter idea has been around for quite a while, but the first one I heard of was one that my wife's cousin made over in Saipan. They were the envy of the neighborhood!
A buddy of mine uses one for storage on his vacant land over in eastern Oregon. They are very secure, but Last year it was broken into and they stole his new quad four wheeler.