Mine has rust spots in the seat rails, apparently in the winter getting in with your feet full of snow will cause some of that snow and salt to get in, it then stays there until it dries. Very visible from the side of the seat when you get in.
I'm also concerned about the door hinge area were water can build and remain there for long periods. Same with the trunk gate there seems to be built in water reservoirs for when you open it so the water and snow builds up there but there is no way for the water to get out?
I think we will be ok with the easily replaceable side skirts. As far as underneath the car It looks pretty new
I have an 03 that I drive in chicago all season so I think I would be likely to begin seeing issues
As far as rust proffing...I used to sell cars and would recommend my customers to get their car rust proofed at least once a year
But all bs aside..If anything it will make the water stay up there longer and damage your frame faster. the water needs to get out...it will just plug it up there longer