Before the advent of stainless steel firearms, we used a coat of silicone car wax on CCWs and hunting weapons. It worked very well. A "hard" wax such as carnuba should do as well, now that the silicone products have gone away. Just be sure that the words "polish" or "cleaner" don't appear in the label blurb, as they usually indicate the presence of chemical cleaning agents or abrasives which would degrade the finish.
Blue Wonder "Armadillo" is a firearms-specific polymer product made for the precise purpose you cited. It costs a good bit more per oz than car wax, but it's very tough and works just dandy. "Renaissance Wax" is another great product developed for use by museums, etc. to protect artifacts from deterioration/oxidation while on display or in long-term storage. I've used it for several years and never had a fleck of rust appear on a treated item. It's expensive per jar, but it takes so little to coat an item that one jar seems to last forever.
Haven't tried "Eezox". The other products have worked well enough for me that the occasion never arose where I felt the need to try another one.