I drilled the front two mounting holes with a #40 on the left rear interior Aerosport Products panel. I will have to enlarge to a #19 and install a nut plate later. I then cut a hole in the panel for the air vent cover. The trim lines were about 1/8" too small, so it took me a little while to enlarge the hole to the correct diameter. I proceeded carefully becuase I didn't want to over enlarge the hole.