Stop obsessing over it. It's not goingt o rust into oblivion from getting rained on. Wash the bike like you do a car when you think it needs it. Towel dry if you so desire.
Clean and lube the drivetrain when needed.

I've cut apart frames that look like they had serious rust and the depth is very minimal. People generally have a lot to learn about the strength and longevity of steel after all the propaganda from bike companies pushing alloy and plastic