mirrors on front wings can be a real pain to align correctly, and many just dont work there. I have only heard from a few owners of sports cars that like them there.
In europe they may be more useful, especially if you are towing something. I think that is why they were added.
As far as mounting, just copy left side location and drill holes.
Yeah, I wouldn't want to mount them on the wing, unless it's the way it was done perhaps, and even then I'm not sure. The mirror of the W115 is really small, and I actually wonder how you could see something when it's installed on the wing, especially with all the vibrations from the wheel and suspensions there.
Actually I can't drive without a right mirror, I find it extremely useful, not just when towing something, but also after changing lanes, or to look for bikes crossing the streets at intersections (they have "green" just like people and come quite fast sometimes, and the law here says that you have to stop), also when parking in the city and so on. Definitely couldn't live without a right mirror.
Still I have the feeling that when mounted on the door, you'd have to turn your head quite far to the right to see what's in it. And that's why I thought some people may have mounted it on the wing. Does anyone have experience with the mirror on the door? Am I right with my assumption or not?