New automobiles are much better in this regard. In the 70's and 80's, if you didn't Ziebart coat the back sides of the sheet metal, they only made it a couple years before rust became a problem.
I've got a fleet of vehicles on the road everyday, most of which are ford trucks. The body's and mechanics hold up very well, we typically run them about 10 years to 250,000 miles or so. The weak link we see is the frame. They have lightened up the frames on newer pickups and they rust out.
Keeping a vehicle in a garage overnight and routine washing go a long way towards making them last a long time.