a conversion unit for a pickup truck long - cab chassis frame , modified to support a regular cab , thereby providing a frame clear length of almost two feet between the cab rear wall and an open front end of the cargo bed . the conversion unit includes a plastic bedliner portion , defined by bottom and opposed side panels , and a self - supporting , integral , forward extension portion defined by an extended bottom panel portion , extended side panel portions , and a front panel upstanding from the forward end of the extended bottom panel portion . a metal framework , embedded in the plastic extension portion , is adapted to be secured to the frame clear length providing an extra - long composite cargo bed . a second embodiment of the unit provides a lower - half opening in one side of the extension portion , adapted for closure by a downwardly opening lower hatch swingably supported on the framework . a camper shell and expandable roof cap enclosure assembly , adapted to be removably supported on the unit , includes an upper - half opening in a shell side wall , adapted for closure by an upwardly opening upper hatch swingably supported on the shell , positioned in matching alignment with the lower hatch . upon each hatch being moved to its open mode , the resulting full height opening cooperates with the expanded roof cap , whereby sufficient headroom is provided allowing a six - foot person to easily board the conversion unit enclosure assembly .