If you keep it in an unheated outdoor shed, would it be better to keep it in a insulated cooler? I have some opened and unopened and on one of the cans it has a price tag of $19.95.

Get ammo cans. They hermetically seal and will work well. Humidity is the enemy, not temperature. They can be bought at army/navy surplus stores and probably online.

cold isn't an issue

heat isn't great but if you can keep it from being over your max ambient not really an issue

mostly you want to keep it dry

avoid swings hot cold in quickly which condenses humidity in the air

make sure the gaskets are good in the ammo cans

MTM is making nice poly boxes and ammo cans with good gaskets in them and you can get them in a larger size.

desiccant packets would also be good if you could

You must have hermetically sealed stuff back when you were a 461, Paul. We used a vacuum cleaner with a piece of small diameter pipe to evacuate the air from the stuff that required it. That was state-of-the-art back when I was doing it in the early eighties.

If going to try to pull a vacuum on it best make sure you have an anti static hose and grounded.