There was a company that made campers to be mounted to a wagon back in the '60's. It was called the 'Tote Motel' by Lite Cloud Campers.. A wagon might be a little more beefy, but it still seems like a LOT of weight hanging off out past the bumper!
Aside from an old ad, and random pics, no real history online regarding the company that made them.
Our family did a LOT of traveling in the 1960's. I've NEVER seen one of these. Without youtube I'd never seen the fifth wheel VW either. FWIW, the VW seems more reasonable now after seeing these others.