Will the fiberglass roof support my weight if I walk on it?

I don't know about walking on the roof, you would be placing your total weight in a small area (read small area receiving rather high pounds per square inches). I have a 2002 Chevy Roadtrek and know the roof should support my 190 pounds - to crawl around the roof which distributes the load over a larger area is one thing, but I would not stand up on my roof. Your roof may be different, but it is also a long way down if you standing and fall.