Gents, I can not stress enough how detrimental storing a firearm in a gun sock or case can be to the finish. Though not applicable in this case, I have had countless stocks through my shop with the pattern of the gun sock or case embedded into the wood finish. Moisture and/or heat being the culprit.
What is applicable here is socks/cases will trap moisture. I can't think of any place with a greater potential of condensation forming on a stored firearm then in a truck. Hot to cold "AC" to hot again and vise verse, cold to hot to cold over and over again.
Other then one of the epoxy finishes on the market or a rattle can of Rustoleum waxing is your best chance of not having that matte finish rust, oiled or not.
Waxing is a time tested way to protect metal from rusting, look it up there's info out there.
From firearms to tools to relics dug from the earth.
That's my professional opinion anywayz...