A powered trailer unit that includes a support frame, and a bed disposed on the support frame. The frame has a first side, a second side opposite the first side, a proximate end and a distal end. The first side has a first guide rail, with the movable wall movingly engaged therewith. There is a mover operatively engaged with the movable wall, the movable wall configured to be moved back and forth along the unit by operation of the mover.