Miss. Code § 63-7-85
In lieu of the tarpaulin provided in Section 63-7-83, a truck, trailer or other carrier with an open top while traveling upon any state, United States or interstate highway in the State of Mississippi and while carrying any load of sand, dirt, gravel or rock shall be in full compliance with Sections 63-7-83 through 63-7-89 provided same is not loaded within six (6) inches of the top of the bed or is equipped with four (4) six-inch (6") sideboards, which sideboards shall be attached one (1) each to the front, back and two (2) sides of the carrier body, and shall remain lowered while the body is being loaded, provided that no part of the load shall extend above the body of the carrier. After loading, the sideboards shall be raised and secured to remain raised during travel, and the space between the top of the sideboards and the top of the load making contact with the sideboards shall not be less than six (6) inches.
Miss. Code § 63-7-85