Plastic bags, vacuum sealed, with VPCI is one way.
Lots of brands, here's one at Midway
https://www.midwayusa.com/product/10...storage-bag-55
Brownells sells metalized plastic bags (zero vapor transmission), with protectant tabs. At five bucks a rifle, the cheapest insurance you can get.
https://www.brownells.com/gunsmith-t...-prod1154.aspx
Main thing to remember is that rust can occur only when iron is exposed to oxygen. Take away the oxygen...it isn't possible for rust to form.