Around here if you start sanding to the bare metal by the time you get to the other end of the panel the part you just did minutes ago already started to rust.
around here if you trap the moisture you get in trouble but as long as it the dry air gets to it then you are ok.
Like trunk floors get rusty if it gets wet under the rubber mat and stays sealed in. I always leave trunk lids popped for that reason because even if the back window leaks or something, as long as it can breathe, it will dry out.
Same for engines, if you leave an engine outside with the heads on and it gets water trapped in the cylinder, big trouble.
But you can leave engines out with the heads off and even if it gets rain or a bit of snow, it will dry out right away and be fine.