If the panel is flexable, I'd be worried about paint problems. Today's paint has a decent amount of give if you tweek it once in a while, but it will not take well to the panel flexing around regularly, such as vibration/flex from normal driving.
I repaired NASCAR fenders and hoods regularly for 4 years. We've stood on the hood for photos without causing any damage. Had mechanics climbing over the fenders to access the motor. The car's seen decent side swipes that left no severe glass damage (paint damaged and rubber scuffed - yes). *I* would recommend against flex, and add support. Our fenders were 1/8 thick, and the hood was the same with a few ribs where required. A curve in a rigid glass panel will add incredible strength. You can lay in aluminum mounting tabs to prevent the attachment points from breaking away. You will end up with a panel that won't dent like metal, is light weight, and is plenty strong enough for your friends to lean on.
