You could oil well, wrap in paper, then in plastic.
The reason for the paper is that many plastics will slowly dissolve in oil.
Butcher paper or something along those lines.
I do not have a specific paper that I know would be low enough in acids (if that is even a concern in paper anymore), perhaps someone else has more specific info.
I know they used to make oil paper just for weapons and such, but have never had a need for it, so I am clueless.
One thing is, if it is just handguns or the rifles are not too long, concider a large plastic trashcan to keep them from floor moisture (can add several of the those dessicant packs before closing up to keep it low in moisture).