I installed a couple of panels on my son-in-laws toy-hauler. We ordered the z-brackets with the panels. I didn't like the mounting and converted the brackets into L-brackets. They are made from soft aluminum and can easily be straightened. The roof has a rubber deck. It was easy to find the rafters with a stud finder. One screw into the stud is adequate to hold bracket, but first pre-drill the screw hole. The fewer holes into roof the better off you are. Each 140W panel is held by 4 brackets. I used Dicor to cover the brackets and screw heads.
Sal