Does that camper have an aluminum frame? If it is built like my 2001 Lance 915 was, it has a classic wood frame and an aluminum roof. There is a relatively solid layer of plywood under the aluminum.
You could remove the interior decoration of one of the roof vents; that is pretty easy to do and exposes the layering/construction of the roof.
Depending on the thickness of the plywood, you can bolt the solar panels directly to the roof with some short wood screws, without the need to find additional support.
Seal all holes / screw heads well, goes without saying.
You might also consider to mount an air dam of sorts in front of the panel, so the wind doesn't get underneath it while you drive.
