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....
What about using sthe pray-on coating used to preserve aircraft in storage? That may work a one of the barriers. Regardless, in my plan, the container does not come in contact with the soil. Once on the foundation, a wall of cinderblocks is built around the cluster and earth is then filled-in against the outer cinderblock wall. I am working on what to use to cover the top of the cluster.