An apparatus for covering an open top of a transportation trailer container, such as a chip train carrying wood chips, is provided. A flexible cover (e.g., tarp) is deployed and retracted using a roller moved overtop of the container using pivotable arms. A recessed region houses the base of the arm and associated components. A secondary cover covers the recessed region and is biased toward a cover closed position. An actuating surface associated with the arm pushes the secondary cover to a cover open position. Other features include inwardly angled container sides, a foam sealing member integral with the flexible cover, the secondary cover closing when the flexible cover is both fully opened and fully closed, channels between the recessed region and the container, narrow and/or sloped surfaces, and a retaining hook for capturing a roller connected to the arm.