Use 'Sack-Ups' as gun slips/socks. You can buy them at Sportsman's W/H in six-packs for <$30. They are heavy & silicone treated, as good as you can get for the purpose. On the floor use some astro-turf type carpet like you see inexpensive plastic entry way foot wipes being made from, the kind that has multiple plastic feet protruding vertically from the surface. Stand the sacked up guns muzzle down w/the muzzle slightly more foward toward the vault's door. They can go adjacent to one another w/no problem. You may wish to remove the bolts from bolt actioned guns and the operating levers from semi-automatics. Place those parts on the top shelf, but on a plastic roll up type cookie sheet or a piece of thin gauge Lexan, you want no metel to metal contact. Air can circulate under the carpet's 'feet', so no issues with contact causing rust blooms, no need for any special racking w/the socks. Vault is secured [bolted] to something I would hope, so no need to worry about it getting tilted, yes?
Stay away from:
* foam, it deteriorates and can a real PITA to deal with.
* wood, it has tannins/acids/moisture & will cause rust blooms
* metal to metal contacts, electrolysis can take place,even w/seemingly similar metals
* leather, Daryl already explained [tannins/acids]
* untreated cloth: old socks, T-shirts, sheets, etc. .. they may have been laundered w/chlorine bleach = BAD, over time. Any trace is also hygroscopic.
* laundry rooms or salt water acquariums, both present horrible corrosion risks. Put the vault somewhere else!
Hope something here is of use to you.
