What is the best storage for cartridges?

I can only guess, but, nitrogen is a non-reactive gas, so it should be good for preserving cartridges. I think airtight should be good enough. The problem with exposure to the air comes from constantly introducing new reactive compounds (principally oxidants).

Are talking about short term storage when the cartridge is out of rotation OR archiving and preserving a cartridge over a LONG period of time?

Brf - depends on the number of carts you are using. In my case with about 40 carts using on 12 arms installed on five TTs I sometimes change carts frequently and sometimes not. So we may talk about a storage box on the long run, maybe for up to 30 carts.

best & fun only

I decided to build a storage case which can be used as a humidor optional. will show the final result in about two weeks. Thanks again for all the valuable hints. Stay tuned

best @ fun only

today the Bavarian Humdior has seen the light.
I put two images on my page. the humdor is the small unit below...

best & fun only