A panel system attached to a truck box is provided. The system has a pair of side panels attached to the truck box and moveable between an extended position above the truck box and a stowed position within the truck box. The system also has a rear panel associated with the pair of side panels. The rear panel is configured to retain the pair of side panels in the extended position. The pair of side panels is configured to retain the rear panel in the stowed position. The system may carry more cargo and be easy to install and use.