Originally Posted by F&J
Edit; There should also be 2 small exterior portholes on the outside of each of the bedsides. Then there were 4 brackets that were hand-screwed into those holes for chaining the camper down. Back then there were rumors that those tie downs were not legal in some states because it did not hook to the chassis.
A bit later in this generation of trucks----a steel tube was mounted to the frame under the bedthat extended to the outer body. A slide in bar was slid in and and retained with a clevis pin. Now the camper was tied to the frame thru those same holes.