I hear it isn't necessary. I talked to someone once who said putting your ammo on a big bowel rolling it around as you add a few squirts of WD40 will prevent any corrosion if your ammo can leaks. He says all you really need is a waterproof ammo can, the WD40 is an extra layer of protection but is not necessary.

NOTE: Too much oil will cause many rifles to malfunction since it will dry onto the shells eventually, only apply a light coat if you do it at all.

Vacuum sealing is a waste of time. That is to protect things from air and water, all you need to do is protect it from water. Air doesn't hurt ammo unless it is like in a sauna.