OK, I leaped before I looked. They're everywhere! I guess the only question is will the drip rails support everything? They weigh about 200 lbs. With 2-3 people you're talking about another 450 lbs. Seems to me to be a lot.
IIRC, the roof was reinforced by the floor, to prevent denting. But I'm sure that only part of the tent's weight is on the roof
As long as your clamps securing the apparatus to the drip rails are good, I would trust it. The outer section of the roof where it meets the drip rails is one of the strongest areas of a car body.......The curved shape also contributes to that strength.