Very good topic! About 6 months ago, it hit me all of a sudden, that it was pretty dumb to leave several thousand dollars worth of knives sitting on a bookshelf. The next day I got 3 fireproof safes and began storing them there-theft is not the only danger. I always tuf cloth all before any anticipated long term storage, even stainless. The only knives I keep sheathed are RJ Martins in the mahogany lined sheaths, all kydex and leather stays away from the blades.
One more thing, if you have a pile of $ into your knives, it's imperative to have photographic evidence, even documentation from sales or trades, obviously stored in a different location. There isn't an insurance company in the world that would believe the cost of most decent collections without some type of proof.
pojim