Don't you think that the case, bullet and primer creates an air-tight seal?
Yes, it does.
Ammo has been stored with no real forethought as to longevity for decades at a time and continues to perform flawlessly.
It's simple, if you're worried, get a lubricant that's rubber friendly and use that. They aren't that tough to find.
Personally, I think you need more to worry about if this sort of thing is even on your radar but if you feel the need to worry about it then fix it.
Rubber protecting compounds are cheap and plentiful. Get some Lexol or Armor-All or McGuire's protectant and sleep well at night.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.