Have you ever tried sealing primers?
I have and its a pita. I could never get it right. Unsteady hand with a superfine brush didn't work. Painting the entire bottom of the case head was worse. I gave up on it. I know what you're after though, just a leetle extra peace of mind and confidence in your long term storage ammo.
I seen a vacuum sealer on tv that uses roll bags. Seal one end, dump in your (ammo) food and as it seals the other side it sucks the air right out of it. You can tell at a glance if its broken the seal. I want one. 210 rnd battlepak anyone?
Primers, clean brass that wont oxidize, even 1lb cans of powder, and ammo of course.