Great pictures!
Yes there was at least two manufactures that would build slide in station wagon campers, as well as larger units for pickups. For that manufacture, the tailgate was folded down, then the camper attached, with some sitting on the roof.
The pictures above - this built in class C is much more stable than the slide on type, yet you are sort of stuck with it on the car all the time. I would guess a C-30 based truck chassis would have been better weight wise, and stable too. Yet some did not want to have a "Truck" front end or cab to ride in, so this is a little more car like drive, and what the wife might accept as a vacation vehicle.
Great memories.
Fred.