What is the best storage for cartridges?

Is a humidor really the best storage vessel? I would opt for something completely airtight. The most obvious enemy of a cartridge is airborne pollutants, such as ozone. Ozone attacks the rubber components of the cartridge suspension making them brittle.

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).