I've actually been thinking about long term coin storage a lot recently. The biggest issue is air penetration. The second biggest issue is breakdown of the packaging, primarily through UV radiation. Which is all very similar to long term storage of food. This leads me to think for long term storage, vacuum packing with an O2 absorber, inside a mylar bag, inside a safe, in a climate controlled room of some sort would be best. The downside is you wouldn't be able to look at the coins very often because you'd have to do all the resealing .
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.
