I too live in a high humidity state. Georgia. Here is an old woodworkers trick for applying a thin coat of oil to metal which works for me.
It is just a worn out towel cut to size, rolled, and then inserted into a small can. You then add oil, in this case 3-in-1 oil - but only enough to produce a very thin oil coating. I coat barrels, locks, plane soles, machine tops and the like with the oil, it is quick and easy and I have had zero trouble with rust. Generally I leave my tools and gun parts in the shop all year, even finished guns. About (more or less) once a month I go over them with the Rag Can.
Others mentioned your possibly being one of those who naturally have a higher acid "fingerprint," this is likely so handle the metal with a clean rag or gloves while oiling.
dave