In researching upgrades and new material for this site, sometimes I come across the strangest things.
From 1970s ads:
Fifth-Wheel Trailers usually hitch onto a pickup-truck cargo bed, but this new Shadow design from Harmon Industries, Warrensburg, Mo. tags onto a passenger-car rooftop. A removable steel plate, bolted to brackets along the roof gutters, take advantage of the roll-resistance built into modern roofs to firmly anchor the trailer hitch. Great maneuverability and easy tow handling are claimed for these rigs. Models of 18, 23, and 27 feet are being produced, and unfinished units are available for extra savings. Shell for the Shadow 18-foot Mini will start at about $1700; price is $6500 for the completed 27-footer fully equipped. Driver reports indicate the design is aerodynamically suitable and does not buffet at speed or in strong winds.