Check out this weird Beetle/Camper combo from 1974. The trailer section attaches to a latch on the roof of the car in a slightly dubious manner. It's nicely colour matched to the Beetle though!
The great thing about this set up as opposed to using a traditional tow bar is that the range of movement is expanded. The driver is able drive freely without worrying about jackknifing the trailer. It hard to explain but it all makes sense if you see a video of the trailer in action.