Where are all these corroded aluminum body F-150's you all are referring to? I'm in the snow belt since forever and have yet to see one.
Maybe you just haven't noticed them. I live in an area with high snowfall, and copious amounts of salt are spread on the roads all winter long. Look around, ask people in the automotive service industry, heck, there are probably pictures online.
The point is they certainly can rust and/or corrode. My advice is to take all steps to limit rust and/or corrosion in a highly corrosive environment, as is suggested in every vehicle owner manual I've had.