I've sent "art" back to Europe using a sea container; the objects were commercially available and were part of a design show. I would never contemplate using sea containers for fine art, since they are sometimes lost in rough sea conditions. There is also risk in the loading and unloading of the container at the dock; containers can be dropped anywhere from a few feet to more than 25 feet.

It's a good idea to inspect the container first by seeing if you can see daylight from the inside. If you do find that it is less than water tight, caulk should be used to plug the cracks; remember that the containers ride in stacks on the ship and are exposed to the elements. I also purchased the expanding foam that comes in little pouches to tighten up the load which was cheaply constructed wooden crates. I locked the crates in by screwing dunnage to the floor of the container and used the expanding foam to lock them in place. I also purchased ratchet sraps to take advantage of the hooks that were at several locations inside the container.

It is a very economical way to ship if you are not in a hurry for the contents to make the voyage and if you feel the money saved justifies the risk.