I have made a set that attatches to the ball mount (2" angle iron welded to a 2" long pcs of hitch tube, 1 semi mud flap cut in half). Works well, and cheap compaired to the one at camping world. The one thing I hated about this set up, it sit behind the rear bumper and at approx knee height, you will run it to it and it hurts.
Next set I made mounts just in front of bumper (can't walk into this set up), yet still hangs far enough back from the tire to catch any mud, rocks, ect.. I made brackets that are attatched the the hitch/frame, then on the mud flaps themselves, I attatched a tube that plugs into the bracket to hold them in place.
They are removable when not towing, work VERY well at keeping rocks from hitting whatever you are towing.
Click on my link in sig. goto my truck photos, there is a photo of my removable mud flaps.
I was only into the set approx $20.
What ever you decide to do, don't go with the 'grass skirt' style, at hwy speeds they just whip in the wind and will not stop much at all. You need a good wide heavy rubber flap.
'01 F350 PSD 4X4 CC LB SRW, firestone air bags, bilstien shocks, superchips 60hp, 4" cat back exhaust, front end leveling kit, aux trans cooler
'00 315 wanderer, Honda EU2000