It is the weight. Because the rig has to weigh enough to resist the 'Lift' that comes from air flow.
The hood on my SUV is pretty heavy.. But, because of the aerodynamic design of the front end,
if the hood latch isn't engaged, and there is a gap 10 or 20 mm wide, a 60 mph wind will lift the hood.
https://www.youtube.com/results?sear...+while+driving
Look at the top and bottom edges of the array.. Do you see the gap?
Wind from the south hitting that bottom edge reminds me of an unlocked car hood.. But not too bad.
Wind from the north side flowing over the peak, will create lift, at the top of the panels..