Ice is a different animal when it comes to corrosion. Remember that car they buried in the time capsule in Tulsa? It was new and when dug up found to be a total loss. If those crates are water tight they might have something.
If the crates were made out of wood, they're not going to be water tight for long in the wet, humid environment of Burma. Being entombed in cosmoline is about the only way those planes can survive intact this long.