Abstract: An extendable and retractable cover for use on gondola railroad cars, preferably provided as a kit for retrofitting existing cars, including elongated runners for attaching to the top of longitudinal walls of the gondola railroad cars, the runners including at east one slidable surface, for supporting and permitting transport over the surface of a plurality of tarp supports, which extend across the lateral opening between the sidewalls of the gondola railroad car. The supports are adapted and configured to slide over the runners while enclosing an edge of the runner so as to engage the runner and retain the vertical position and orientation of the supports during transposition across the surface of the runners.