You can reach up there and use fender washers and nuts too. I would sugest getting the factory inner brackets they make a much sturdier mirror. I can't remember off the top of my head what they are called but are a type of sqaush nut. They are made from rubber and have a brass nut formed right into them. When you tighten the bolt down it draws the nut up intothe rubber, hench spreading it out in the hole. I like these better becuase they don't rust, they seal the hole better, and a year or two down the road they come undone unlike the metal ones which sometimes spin in the door.