Certainly the chain is one component to be concerned about with extended exposure. When I was working, I would keep one of my road bikes mounted in the bed of my pickup truck so that I could go on quick rides during my lunch breaks. I kept it locked, so it’d stay there overnight when I’d get home. Obviously there was rain and humidity. It was a CroMo frame, and generally, I tended to the chain, and other components for corrosion. But I never though about the seat post/tube. It never needed adjusting. Then one day after several months of extended exposure…something encouraged me to take the seat off. Otherwise, the bike was in good condition…no frame rust, or corrosion of components. But I wasn’t able to get the post out of the seat tube. I mean I used all the tricks. I even tried pounding it in farther to loosen up the corrosion but it would NOT budge. Eventually I inadvertently bent the frame trying to remove it, and that was the end. I salvaged all the components and used them on another frame. But, I don’t let any of my bikes get extended exposure anymore.
Dan