A trailer for transporting bulk material has a container mounted on a chassis and wheeled suspension. The container has opposing sidewalls, a floor, a front wall, and a rear opening. The trailer further has an unloading system comprising a plow and a plow motor system. The plow is disposed in the container and shaped and sized to span substantially a transverse cross-section of the container. The plow motor system is operable to move the plow longitudinally in the container to urge or push the bulk material in the container toward and out of the rear opening of the container. At least one of the sidewalls comprises a removable panel installed longitudinally along a bottom of the sidewall, wherein an inward-facing surface of the removable panel and an inward-facing surface of the sidewall are substantially coplanar.