I sure would not put too many people up on top! Maybe two adults and one child.... If you have open space, maybe cut out a thin layer of 4 x 8 material. Maybe cut it in half for carrying, or cut to size if a full 4 X 8 won't fit. Then duct tape it together when on the roof. Does not need to be too thick, and does not need to be plywood. But, this would shield the roof fro chairs.
Have a blast,
Roo II is our 04 Country Coach Allure 40'
OnDRoad for The JRNY! Enjoy life...