Which backup camera are you using?
I installed the Voyager Wireless camera just last weekend on my Eagle. The instructions I got from Jayco have you drill holes into the fiberglass and then use the included screws (came with the camera system) to attach the mounting bracket along with some silicone to keep everything sealed up.
The middle marker light in the back had the wiring for power to the camera, not sure if yours is the same or not?
2012 RAM 2500 Megacab Laramie Diesel
2016 Jayco Eagle 284BHBE
ProPride 3P WDH