im not saying it wont fail but in the past i have has cars with tow bars mounted the same way.my 240k 2 door had one mounted to the sheetmetal as such and i towed a car trailer a couple of times with it and it didnt seem to stress the car.mind you it had some healthy 10mm plates as washers about 75mm x150 mm.and the mounting points were spread wide apart and a center brace was fixed thru the spare wheel well so the load was spread over a large area i actualy removed it and put in my next 240 thats how i could tell it hadnt done any damage.that was 20 years ago and the laws are pretty strict now .