Well this is what i had to dig out of the door to mount the mirror. The truck was already painted so i cut the rectangle hole with my drill and dremel wheel and finally drilled and worked it out. the problem is the rectangle hole is about 1/8 or so bigger then the rubber mounting pad. ? do they make a bigger pad or someone with a clever thought, Really don't want to mmess with the paint.

 

You could make a small plate from thin gauge stainless steel and glue it around the hole and slide the mirror arm through it.