One cell carrier I did work for used them for cell site buildings. We built a couple hundred sites using shipping containers for buildings. Get ready to use a lot of tar if you decide to do this. Most of the ones I worked in leaked like a sieve. We had one 40' container in North Carolina that literally had a waterfall coming down one interior wall every time it rained until we bryed the roof.....
The leaking is probably the reason they were no longer in service for shipping.
I guess that it depends on the quality of the container. I have known folks who use them as storage sheds and have not had problems with them. Regardless, I have thought of using several moisture barriers (chemical and physical) because I intend to build a partially buried structure.