All my gaskets are in a wide flat box, some 40yrs old. Only ones that get brittle are the old black stock ones. Always been in non humid environment. I use cardboard between levels. I usually order 10 at a time of whatever I need, I use them up. Head gskts I use copper coat when assembled, they are all fine.
Like Mike says, water the paper ones otherwise they don't fit. Not even new ones.