Ive noticed this on my truck and my moms 3rd gen. that when our roads back where we live(dirt roads) are wet, that the mud will come into the bottom of where the door meets the fender. Im thinking maybe a set of mud flaps?

 

I bought mine with running boards and mudflaps and intended to take them off immediately. However the truck stays so much cleaner that I have left them in place. They really help with mud and road water. However, I'm not sure they will make much of a difference w/ dust. I have the large square ones in the rear and smaller stainless steel ones at the front and the forward part of the rear well. Kurt