Our 1991 Bigfoot
17 came with woefully small mudflaps. In the rain, water and grit covered the aft section of the trailer.
A couple of 18-wheeler flaps were cut up to make larger flaps. They turned out to be too flexible, so the original flaps, quite stiff, were glued to them with silicone. The hybrid flaps were screwed to the body near the original mounting location with an additional lower screw added.
Our friend and mentor HandyBob [Google HandyBob+solar] did the cutting, gluing, and attaching.