it isnt an issue that I have had, but a quick wipe over with oil or wax before storage should sort it. it should be easy and quick before it is removed (rotate a wheel by hand and hold a brush or rag to it) but not a big task afterwards.
My blades were subjected a whole day of rain running down the wall and around all the blades hanging on a screw.
The roof got fixed. I have found no problem with the blades even though they all went very dark red.
Although it would be best to run a piece of scrap wood through to remove excess loose rust before trying to cut a finished edge in light wood.