Don't forget the penny under each clamp, lol.
I've used a variety of battery cleaners and terminal sealants. Grease is greasy, it will get on my shirt, my hands, and others. I lived with a shirt spotted or soaked in petroleum products for years. Grease won't kill 'ya but I don't need any more than is necessary on me now. Dielectric grease is expensive.
I am using the same can of Napa battery terminal spray that I first used 15 years ago. It sprays a red, rubbery spray onto the terminal and I may have to renew it when I clean terminals over the years.
If it was just air that caused corrosion on a battery terminal, we would be living in a sea of rust. The emitting of H2SO4 and sulfur dioxides is principally what causes corrosion. The acidic vapors need to come into contact with the metal terminal. So, yes, your solution of an "air tight" coating is correct.
