From the Louisiana DMV :
"Fenders - Fenders are required on all trailers where the rear body portion does not afford adequate protection to effectively minimize the spray or splash of water or dirt. All fenders must cover entire tread width of each tire. The determinant of the effectiveness of the body to act as a fender and/or mud flap is whether the height of the rearmost portion is one-third of or less than the distance from the center of the rearmost axle. This section shall not apply to vehicles registered as farm vehicles. ..."
Flashing would be the easiest way ... Mud flaps would be COOL and help with not throwing rocks ... !!!
