With the rusty floor section removed, we cleaned the rusty areas with a wire brush on a drill motor to remove the surface rust from all the remaining areas. Then we spray painted the trunk-floor reinforcement panel to prevent further damage. POR-15 is an even better idea as a rust inhibitor. If you must replace the reinforcement panel, consider tacking it in place before final installation of the floorpans. This will save time later. These will require overhead welding, which is a difficult skill to master.