Because of all the air conditioners and other stuff on my roof, I have mine mounted over top of the air conditioners. I also have a 2 inch on 4 ft angle favouring the usual way we park both for rain run off and a bit of angle for better efficiency. I also made them so that I could raise them if we are parked long enough to make it worth while. The wind really is not a problem on the roof. I forgot a small wrench and a 1/4 inch nut and washer on the air conditioner and after 500 plus miles they were still at the same place that I had forgot them.
