I've installed backup cams on a number of my RVs over the years. Most of the cam brackets I've used had 3 holes in the back of them. One in the center that is large and one on each side of the center that are small. The small ones are for the fasteners and the large center hole is to pass the wire and connector into the mounting surface (rear cap).
On all my installs that did not have any existing mount on the RV, I used "Well Nuts and Stainless Steel Machine Screws to attach the bracket to the rear cap. I first however, drill the larger hole for the wire/connector.
On edit: found some install pics -
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