Frame. Frame Cross Members. Body Mounts. Floors (if Applicable). Doors, Handles, Latches, and Hinges. Landing Gear (if Applicable). Rear Protector (Mud) Flaps. Rear protector flaps are not required on a vehicle when the construction is such that complete freedom around the wheel Sheet Metal. Rear Metal Frame. Each trailer and semitrailer, when operated on the highways, shall be equipped with a permanent metal frame attached to the underside of the rear of the trailer. The frame may not be wider than the width of the trailer and more than 30 inches above the highway, and shall be constructed of heavy gauge steel. The maximum The maximum transverse distance from the widest part of the vehicle at the rear to the frame may not exceed 18 inches. Any trailer or semitrailer so constructed and maintained that the body, chassis, or other parts afford the required protection is in compliance with this regulation. This regulation does not apply to pole trailers or trailers or semitrailers when the installation of the frame would prevent operation of the vehicle in fulfilling its designed use. The frame may not interfere with lights or other warning devices. Inspect rear metal frame for: