The ornamental design for a fire-proof storage box, as shown and described.
FIG. 1 is a front perspective view of a fire-proof storage box showing my new design;
FIG. 2 is a front perspective view of the fire-proof storage box thereof, with the lid shown exploded off the top of the box;
FIG. 3 is a top view of the fire-proof storage box;
FIG. 4 is a left side view thereof;
FIG. 5 is a front view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a back view thereof; and,
FIG. 8 is a bottom view thereof.
The broken lines shown in the drawings depict portions of the fire-proof storage box in which the design is embodied that form no part of the claimed design.