I have a 3500 dually too, I put mud flaps on all 4 wheels. I paid under $ 100.00 on eBay brand new. I also put Rock Tamers on (these go on the tow hitch bar. They are solid and not a skirt), Costco under $ 200.00. I DO NOT know if I wasted my money yet because I have not towed yet, so Caissel may be correct. I do know that last year I was on Route 95, in the rain and a semi threw his recap. It went between the TV & TT and caved the diamond plate (option) in on my old TT front. I believe if I had the Rock Tamers then I would not have incurred as much damage (if any) as I did. However, even with the Rock Tamers and the individual mud flaps on the rear tires, there still exist a gap where stones - or other can come back and hit the RV, so again Caissel may be correct. When I stand 4 or 5 feet behind my TV I can clearly see the point where the tire contacts the road and this is the launch point for all debris. I would have opted for the diamond plate had I known it was available as an option. Tom