1. My custom aluminum oil door had some remaining ripples in it, as a result of the way I bent it to match the cowl. I decided to fix this by using a file and a 220-grit sandpaper on a hard block. I was able to completely remove the ripples and also smooth out one of the rivets in one of the Hartwell latches. 2. Sanded the outside surface of the door with 400-grit paper. 3. Cleaned and masked the door. 4. Primed the door with high-fill, self-etching primer.