I will add to this. I am not a fan. I have been at this for quite a few years working for three manufactures and many dealers. I actually work on these, not just hold the steering wheel. ALL of our studies showed the flap will cause air flow issues and will show itself quickly on hot summer days pulling long grades or pulling big trailers. The engine in a coach running the flap will de-rate faster than a coach not running a flap. I can't tell you how many times we would pull over and remove flaps heading to shows and then reinstall when we arrive...just my.02