Its not the towing thats the problem, its the stopping. TECHNICALLY/LEGALLY these motorhomes towing the small cars are also breaking the law unless there is some way of operating the towed cars brakes as most are over the 750kg limit. IIRC the only production car that falls below the weight is something from Caterham.

I doubt these small cars will trouble something the size of a motorhome under braking of course. Its a massive difference to towing a car of similiar weight and size and rely on the just the tow cars brakes for the whole outfit.