When I installed a system on mine, I went over to the roof vent pipe. Pulled the cap off and drilled a hole in the side of the pipe. The pipe goes thru the closet. I drilled a hole in the vent pipe near the ceiling in the closet, pulled the wires down thru there and hooked onto the regulator panel. Make sure to seal all holes in the vent pipe with silicone, and put the cap back on the vent pipe. Then just followed the vent pipe down thru the floor into the pass thru storage and over to the batteries.
I don't think I would be drilling any holes in that fiberglass cap.
2008 Cruiser CF26RK
2013 Ford Eco-Boost
Heavy duty payload - Max tow