A pickup truck having an access door in a side panel of the truck bed is provided. The access door pivots between a closed positioned and an open position. The access door defines an opening in the side wall, the opening being created by the access door being moved from the closed position to the open position. The pickup truck has a cap member, the cap member releasably coupling to the side walls of the pickup bed and having a gap in one side portion thereof, the gap being positioned above the opening, such that the gap and the opening communicate with one another. The pickup truck has an extension body that releasably couples to the access door and pivots with the access door. The extension body is configured to functionally engage the gap in the cap member under the condition that the access door is in the closed position.