I put mud flaps on my Cub 176. It was one of the first things I did. The floor behind the wheels is hard foam with a cloth cover. It will erode away quickly from wheel spray.
Buy oversize flaps. Cut to fit. Screw to support bracket behind the wheel. Prime and paint all hardware or use stainless steel. Plated hardware will corrode quickly. Prime and pant support bracket where you drilled holes.
The buckets in the picture contain insulation. They are to prevent drain lines from freezing in winter.
I wish you good luck and happy trails ahead!