The flaps behind each wheel do the best job in protecting the towed , if the are positioned properly , high enough not to drag.they are the best as they are far enough forward of the rear. The rear full flap needs to be high enough that it never touches and doesn't create a air turbulence that can suck small rocks up and throw them into the towed. My belief is that the rear flap is mostly a appearance item. To make the rear of the coach look nice. Several folks I know who travel gravel roads remove them for the trip.