When I did mine, I made a paper template from the front of the door to the rearmost hole of the mounting on the driver side. It was the full width of that concave from the window scraper seal to the crease where the door goes horizontal. Then I flipped it 180 degrees, laid it out on the other side, and marked my holes. Simple. I didn't do a backing plate on mine (never thought to) and have no issues. It does sound like a good idea though.