The ornamental design for a “post base cover,” as shown and described.
FIG. 1 is a perspective view of the present post base cover;
FIG. 2 is a front elevational view thereof; the rear elevational view, left side elevational view and right side elevational views being identical thereto;
FIG. 3 is a top plan view thereof; and,
FIG. 4 is a bottom plan view thereof.
The broken line environmental structure in FIG. 1 is for illustrative purposes only and forms no part of the claimed design.