I knew a guy that used Vaseline for long term protection on some collectible Browning firearms . It's cheap and worked great . Easy to remove when it's time to resurrect them .

If I may, I’ll add a question to this thread...

What about optics? Shoud they always be removed? If kept attached to the gun, should their lenses be capped?

Thanks.

No need to remove optics for this kind of routine storage. They don't have to be capped, but it's best to do so, because if you don't then you'll need to carefully clean the lenses of the accumulated dust after they're pulled from storage.

re the optics, pull any batteries if they have them,

Definitely true for alkaline batteries, which can and will leak over time, ruining your optic. Not as necessary for lithium batteries, other than the risk of the lithium battery potentially running dead from parasitic drain over time.

The possible presence of dust and other debris is not the only reason to keep optics capped in storage, long or short. Certain substances including polymers and petroleum products can produce vapors that can settle onto optical surfaces and affect their image transmission quality to some degree. I always keep all optical devices capped when not in use.