I've been dealing with a 6qt engine since 2014 and have had no issues using an opened jug of oil. close the cap tight and give the jug a squeeze. It is pretty tight. Not perfectly sealed but pretty tight for moist air to get back in there. Think of the moisture your oil gets exposed to during a 4-6 month run in a rainy location. HUGE compared to sitting in a bottle in a unairconditioned garage. If its an attached garage, its semi airconditioned. if you are really paranoid, bring it inside so the temperature swings are very low and the AC keeps the humidity down.
I'm in Texas with super hot summers and my stash is in a detached garage. 120 degrees in august is not unheard of. I'll looks the same from the first quart to the last.
An alternative that takes some math is to rotate the oil. buy two 5qt. pour 5 jug then 1 qt from the second. Then next OCI pour the 4 qts (oldest) first then 2 qt new. and so on. That way your OLD oil is never more than 2 oci old. Not necessary since I have used a open jug 2 years old with not degradation of the oil but if it makes you feel better. there you go.
I'm in Texas with super hot summers and my stash is in a detached garage. 120 degrees in august is not unheard of. I'll looks the same from the first quart to the last.
An alternative that takes some math is to rotate the oil. buy two 5qt. pour 5 jug then 1 qt from the second. Then next OCI pour the 4 qts (oldest) first then 2 qt new. and so on. That way your OLD oil is never more than 2 oci old. Not necessary since I have used a open jug 2 years old with not degradation of the oil but if it makes you feel better. there you go.