If you take normal care of your air rifle I think the only liability is the scope and barrel bore. Good scopes have a positive gas pressure inside to keep out moisture and stop fogging. Would be nice to have a stainless barrel like a lot of firearms today. I work on a lot of airguns and it is quite rare to see a badly rusty barrel bore even on 100 year old types. They usually have rust on the outside through total neglect of just a simple wipe over with oil. When I was in the Royal Marines I often took my SLR into the shower and took it apart to clean off mud before drying, oiling and re-assemble. Was always complimented on its condition after inspection. Even after a total soaking a rifle should not deteriorate if basic care applied.

Baz