I doubt you'll find wood in the fiberglass roof sides.
My fiberglass roof (mid-nineties design) has a few wood stringers fiber-glassed to the underside of the top but not on the sides.
My awning is attached with 3 brackets on the passenger side of the van's fiberglass roof. The aluminum brackets are bolted through the fiberglass and have a metal backing plate on the inside. Some vans will have wood backing blocks.
Some vans had awnings brackets installed with rivets but I've read a few reports where a rivet ends up pulling through the fiberglass. If you have to do it that way then try to find a rivet that expands very wide on the inside. A "blind peel" or "banana peel" rivet might spread the load really well. Caulk any holes well to prevent leaks.
This pdf file shows how the awning was installed on Roadtrek vans in the late nineties and should give you some ideas.