I've used a Bore-Store treated storage bag since around 1993 for my handguns.
There a few milspec & gun industry brands that can protect your firearm.
I'd add a light coat of Eezox, LPX or Weaponshield & inspect it from time to time.
See
www.Brownells.com www.Deltaforce.com www.Natchezss.com www.Sportsmansguide.com .
CF