Eh, my grandfather was a HUGE coin collector. He kept most of his stuff in the original packaging in a standard fire/water proof safe in the basement. When I had to start liquidating some of it after his passing everything was still gorgeous besides the coins that were loose, and most of the collection was made up of items 20 years or older.
Tamo's suggestion would probably work wonders, but I think you'll be able to get by with keeping things in OMP in a safe with a moisture absorber. If you have coins that aren't in a capsule, get Airtite capsules.