I live in a heavily salted and brined area and have not found it to be that bad. We have Winter driven 1991, 1995, and 2002 vehicles in our fleet. The '91 (277k miles) has had the most work, with sections of the floor replaced as well as having one of the frame rails cut open for repair, plus some cosmetic wheel arch work done. One small hole in one strut tower that I just keep oiled down which has kept it from spreading. The '95 (129k miles), every couple of years I crawl under it and scrape off loose undercoating/paint, use rust primer, repaint, re-undercoat. No sheet metal replaced yet. One strut tower does have some bubbling and bears watching (and oiling). The 2002 (179k miles), no work done one it ever, but there's some cosmetic wheel arch rust I'll probably have cut out and replaced in the Spring...
Our cars are pretty much white with salt from late November through March/April.