For rear I use for 18 wheeler truck mud flaps(wide) from auto part store and maybe need to cut one side vertical so I cut flap face inside,(clean look from outside). and front use regular car mud flaps, here is my RV with rear flaps, Feb 21, 2011 https://motorhomemodification-usa.blogspot.com/search?q=mud+flap
As you see in above photo I have reinforced L bracket at front and rear of both tire
J 1990 Toyota/Winnebago V6 rear bath