no matter what kind of protection that may be applied during transit, there is nothing you can do either way. Its how we import cars. Also I highly doubt that the cars are sprayed with anything at all. Once a car is painted, it is then put through some sort of baking process. The 3 week voyage on a boat will do hardly anything to the duco.
Also, after making the deal with mazda and signing on the dotted line, they offered me a special protective coating which cost over $600 and supposedly give greater protection. So with that in mind I dont think that mazda puts any protection during the boat trip......