I have several NIB guns stored in vacuum sealed bags. They have been like this for about 5 years now. I have changed bags twice in that time. Before sealing them, they were sprayed with a long term storage oil that dried to form a film on the metal. I dont remember what the name of it is, but it has worked just fine in a high humidity environment. I agree with Dfaris, the plastic needs to be " dried out " before use.