Ok, time for wind tunnel testing... on a vibrating platform. Anyone want to volunteer their RV? You could tape a dozen streamer tapes all over the panels and mount a GoPro to watch the effect.
If one was really concerned, it would be easy enough to build an air dam or deflector in front of their panels. In my case with two large panels mounted lengthwise,one behind the other, behind one of my air conditioners, I think there is very little chance of wind lifting them off. I'll admit, on my first long trip I did climb up there and check them at every stop.