Gravel roads will do it and break back windscreens as I found and so-
http://www.myswag.org/index.php?topic=25391.msg391612#msg391612Modified that since with plastic pulleys to allow the bungee cord to adjust evenly on tight turns and you want stronger stainless steel lashing hooks on the bar as I discovered. Also poly tarp is the go as mud and clay won't stick to it, unlike shadecloth where some find the clay buildup weighs their stonestomper onto the ground and stuffs it.
Bought a HD Oztrail 6'x4' tarp (the ideal size) and will get that modified for the right eyelets and that sizing would do any camper when coupled with the rubber flaps. However on gravel roads I've found it's the flaps that do most of the protecting, but nothing stops the speed jockeys overtaking or coming the other way. Galv chassis always for mine and now all I have to do is stop the dirt and gravel getting into the back of those rear stabiliser arms Jayco have but that's from the camper wheels.