Is sealant effective/useful for long term storage?

If so, at what point, 5, 10, 15, 20, etc years, is sealant advisable?

What is an effective and easy to apply sealant?

LC once fired cases, CCI450, Hornady 68gr HPBT w/cann, TAC

Thanks!

Possibly a better option is VCPI paper.
This is how industry and the military now do long term storage.

The paper gives off a vapor that drives out air and surrounds the items with a vapor that totally prevents rust, if properly sealed.
For ammo, put it in a USGI ammo can after you inspect the rubber gasket to insure it's good, drop in a sheet of the vapor paper and close the can......good for many years...........

https://www.brownells.com/tools-cleaning/general-gunsmith-tools/shop-supplies/gunwrap-paper/

It may stain nickel and brass if it's allowed to come in direct contact, but kept off, should be good, and any staining wipes off.

Under names like Z-Rust are special "hard" plastic bags with the VCPI in the bag for storing guns long term.

Wrap around guns, tools, other steel valuables for protection from moisture and rust. 1 square foot of paper protects 1 cubic foot of space. Tests show 10-15 years protection when steel parts were wrapped in GUNWRAP, sealed in plastic and stored in a cool place. Will not damage bluing or steel. Not recommended for aluminum, silver, brass or copper.

I used to seal around the primers on my reloads, mainly because I was color-coding the weight of the charge.  Light .38 Special was blue, hotter .38 Special was red, etc.

If you are trying to waterproof ammo you might want to put some around the bullet before it is seated, and seal around the primer too of course.

In general I'd advise against adding sealant.  It will come off and become debris in the gun.