Optimum cartridge storage?

I'm one of those nuts who once they like something - they want a spare on hand. The Slindy modified Rabco/Oracle I am using sounds absolutely wonderful with a Denon DL-301/II installed in it.Unfortunately the friend of mine who commissioned this mod had some peculiar ideas that do make it a ergonomic nightmare - sooner or later - I will break the stylus on this cart.
Question is this: What is the best way to store a on hand replacement cart in case I get lucky and it sits for a number of years before i need to use it?