Yup, environment plays a factor no doubt. OP, here are a few articles that might help select a product for such storage in the future:
Corrosion Protection Products for Rifles, Shooting, Benchrest Competition, Varminting and Firearms Storage
Gun Cleaning Clinic: Knowing the Limits of Rust Preventatives | World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools - BROWNELLS
The Gun Zone -- Corrosion Test
Corrosion Protection Products for Rifles, Shooting, Benchrest Competition, Varminting and Firearms Storage
Gun Cleaning Clinic: Knowing the Limits of Rust Preventatives | World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools - BROWNELLS
The Gun Zone -- Corrosion Test