Tarp enclosure system

A retractable tarpaulin cover system includes a tarp cover, plural spaced substantially U-shaped bows supporting and connected to the tarp cover, movable carriages operably connected to lower ends of each bow, and a tensioning mechanism which moves an end one of said bows toward an endmost position thereof to tension the tarp cover in an expanded position of the cover. The tensioning mechanism includes an elongate brace arm having an upper end which operatively engages an upper or intermediate portion of a vertically extending leg of the end bow, a transmission device which operatively supports a lower end of the brace arm and rotates the arm in a longitudinal direction of the cover system to thereby also move the end bow in the longitudinal direction of the cover system, and a coupling which detachably connects the lower end of the brace arm to the transmission device.