This is my take on the large flap accross the rear since I have one. I tow 4-down and this is the good, the bad and the ugly.
The good - The flap does prevent stones thrown from the tires when traveling on paved surfaces and good roads. Also any larger debris is deflected. It does look good with the chrome or stainless logo, especially when clean.
The bad - When traveling on dirt or unimproved roads as well as gravel campground roads. The flap can touch the ground and actually kick up rocks and debris that would otherwise lye harmlessly on the ground. These things can throw a lot of gravel at 10mph when dragging.
The ugly - Depending on where and how it is mounted it can be a PITA when leveling or entry/exit where there is a quick rise/drop. On mine due to it's mounted position, even though it hangs on two short lengths of chain, it can get caught between the hitch and ground in a standing position. This binds it up as the coach goes down and can bend the pretty, shiney insert all to h**l. I've had to straighten it several times, now I have learned to have myself or my wife hold it back while the other levels the coach to prevent this. Highway drop offs are just luck of the draw whether or not it gets bound up or not. But I will say that most times that it has happened exiting an area I also had the exhaust tip touch down and bend slightly. Straightening these once or twice a year has become one of the characteristics of this particular coach.
2007 Newmar Kountry Star 3914, ISL400
2001 Jeep Cherokee toad, M&G brake/2011 Jeep Grand Cherokee Overland