Give it a good coat, inside and out of Breakfree COLLECTOR oil. This is not the same as regualar Breakfree. It forms a slightly waxy coat and is designed for long term storage.
Then instead of a regular plastic bag, use a
Poly gun bag. These bags are infused with VCI and will deter rust in areas you couldn't cover with the oil.
I have some guns that have been stored for 15 years using this combo and no rust yet.