I live about 3 miles from the Gulf of Mexico on the Florida west coast... I've been a practical shooting competitor since 1980, and we shoot matches in some pretty miserable hot and humid weather... Birchwood Casey Barricade (formerly called Sheath) has been my go-to for surface protection , and Mercury Outboard Quicksilver 2 stroke racing oil for a lubricant as it dissipates carbon well... for very cold weather (for me anything below 35F) INOX nr 3

the QPQ carbon nitride surface treatments seem to be pretty corrosion resistant

I do have desiccant packs in the gun safe