I would be willing to bet there's a connection with the early 1970s Born Free truck campers made in Humboldt, Iowa, not far from where you bought the truck. The company was founded by John Dodgen, and the campers featured a tag axle referred to as the Dodgen tag axle. Perhaps your truck was a prototype for another idea he had.
https://www.rv.net/forum/index.cfm/f...print/true.cfm