We had a big spool of 20lb when I was a little kid, in a dry corner of a fairly deep basement.
We still had about two thirds of it when I learned to drive.
My dad had half of it when I visited my parents at about 20-21.
Last year he called me to say he'd run out so he'd bought more, and did I need any line, because he had a full spool again.
If a spool of line from 1980ish still works after 35 years without a lot of temperature variation and no sun, I'd go with that for all my storage, personally.