Our approach is to stop gravel as much as possible at the source. Though many tow vehicles come with 'mud flaps' they are typically not low enough. Our goal is to stop as much as possible at the wheel well. That usually means extending the flaps so their bottom edges are close to the ground.
On our motorhome we found the continuous solid weighted flap to be better than the brush type.
On our Scamp
the grey tank extends down and we cover the leading surface with foam. Not for appearance, but for protection. A friend had his cracked by a stone.