The ornamental design for a storagebox, as shown and described.
FIG. 1 is a front and top perspective view of a storage box, showing my new design;
FIG. 2 is a rear and bottom perspective view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a rear elevation view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a right side elevation view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof;
FIG. 9 is an exploded view thereof; and,
FIG. 10 is an enlarged view of a portion indicated with numeric 10 in FIG. 1.
The broken lines in the figures illustrate portions of the storage box that form no part of the claimed design. The dash dot dash lines in FIGS. 1 and 10 are for the purpose of depicting the boundary lines of the enlarged view and form no part of the claimed design.