The ornamental design for a retractable truckboxcover, substantially as shown and described.
FIG. 1 is a right side elevational view of a rectangle truck box cover
showing my new design in extended condition it being understood that the
left side is a mirror image thereof;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a right side elevational view thereof in retracted condition
having a retaining strap for holding the cover in its retracted state, it
being understood that the left side is a mirror image of that shown.
The top of the truck box cover is understood to be flat and unornamented,
and the broken lines in the drawing are for illustrative purposes only.