Just look what they use in the back of a pickup truck for a true 5th wheel trailer. Rather stout.
if you brake on a corner the car will flip. the load needs to be applied as low as possible to reduce the overturning moment.Although the idea looks cool enough for some sucker to spend money to develop it. kind of like that flying car that looks cool but doesn't fly.
The tow car in this case already had a name that VW never endorsed. The Flip It! So now you can attach a trailer to the base model and get extra roll when you roll. How cool is that? This trailer has to be made out of Crete paper and cardboard and would likely collapse in a good rain. What do you think 600 lbs with wheels and axle?