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.
I have heard that you can buy them in Jersey for ~$200 apiece.
Moving them is more expensive.
Yeah, a good French drain, if possible, along with coating the containers with fibered tar or melted on bry, then wrapping with a couple of layers of 6 mil plastic around it would probably do it. We did a couple of buried vaults for the radio gear out of shipping containers when zoning became an issue. That method seemed to work well for at least a couple of years. Can't say much beyond that because I moved on to greener pastures.
My farm is in a narrow valley next to a river. Pretty much tornado alley. The house there doesn't have a basement, so I've thought of doing something similar for a storm shelter. One local guy here who makes concrete septic tanks also sells a storm shelter made from a 1000 gallon septic tank mold, only with a door on one end instead of in the top. Good and heavy, just what you want in a storm shelter....