The Sport Trac is substantially different from the Explorer, which has been the best-selling SUV for nearly a decade. The Sport Trac has a longer, stiffer frame, tougher body mounts, larger front brake rotors, and a cargo bed made primarily of - get this! - fiberglass-reinforced plastic. Say goodbye to dents, dings, rust, and bedliners. The tailgate and rearmost box pillars are still built with steel, however. A clever device called the Cargo Cage is attached to the back of the box. Flip it forward and it fences off the cargo box's rear two feet. Or, drop the tailgate, flip the cage back, and stretch the 50" bed to twice its size.