The previous owner of my Roadtrek had a solar panel installed on the roof. I think it is a 15 or 20 watt panel.
It's a pretty neat job. No extra holes in the roof. They used two of the air conditioner cover holes.
The wiring goes into the a/c area, then down the side.
One hole is drilled for the wires behind the door.
The controller is mounted in the "trunk".