My stepfather had an '84 Mazda pickup to replace the old '72 F-100. That was the last year for that body, which was the same body the last Ford Couriers used before the Ranger replaced them.
The Mazda had serious rust problems, and this was in southeastern Virginia, which doesn't see too much road salt. The bed had rusted underneath even though it still looked mostly clean from above. One day I was loading something in the bed, dropped it, and it punched through the bed floor because of the rust underneath. Soon afterward and just after my stepfather passed away, the engine crapped out (I think valvetrain). I hate to think of what might have been going on with the frame.
The Japanese pickups of the '70s and '80s were rustprone. The Datsun and Toyota pickups might have been better at the time, but those have few survivors too.