As for plastic bags; I've stored firearms for years in sealed plastic bags, with just a light film of oil on the metal. But I put a silica gel pack in the package before sealing it up.
If the link doesn't show, go to Cabela's web site and type in "silica gel" and you will find the convenient, reusable packs:
Cabela's -- Hydrosorbent Silica Gel
Edit: Additionally, disassembling it and coating every part with grease, before sealing it up in a plastic bag with silica gel will give you protection even if the bag were to fail and it was exposed to moisture (just in case a tornado hits your house and scatters your belongs, along with this pistol, throughout the neighborhood).