The full width rock guards is tied to how low they are to the ground. When the suspension on your RV goes up and down, it the guard is mounted too low, then it will drag the ground and send a shower of anything on the road back on your tow. Especially can be a problem on gravel roads or in areas of road construction. ON a normal paved (clean) highway, it isn't usually a problem it if hits the ground. Most of the time on pavement it will be lifted somewhat by the wind under your rig as you run at highway speeds.
The mud flaps, whatever you want to call them, that are mounted behind each rear set of tires, when properly mounted the correct distance behind the tires tend to work better. I have always heard that the mud flaps should be 1/3 of the wheel diameter off the ground when at travel height. So a 22.5 inch wheel should have them just over 7 inces off the ground and a foot or so behind the tire.
Now these guards will take care of most of the rocks your rig throws up, but most vehicles you meet going too fast, will be spitting rocks out the side to some degree. Stand beside a gravel road sometimes and watch where the rocks from approaching vehicles end up. (don't stand too close or you will be wearing them)