Here a picture from the back side.
I only used the original bolts. The flaps are bigger and will catch more wind but I think it will be strong enough.
There is a possibility to add a longer screw through the flap into the black cover plate.
I thought of that, but now I think it is not needed.
I did not test it on the German Autobahn yet. (Which I could easily do because Germany is only 4 km from my house in the Netherlands)