FIG. 1 is a front, bottom, and left side perspective view of a mounting base showing my new design;
FIG. 2 is a bottom plan view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a front elevational view thereof:
FIG. 7 is a rear elevational view thereof;
FIG. 8 is an additional front, bottom, and left side perspective view thereof, the broken-line disclosure being for illustrative purposes only and forming no part of the claimed design;
FIG. 9 is an additional front, bottom, and left side perspective view thereof, the broken-line disclosure being for illustrative purposes only and forming no part of the claimed design;
FIG. 10 is a top, front, and left side perspective view of a second embodiment thereof, the broken-line disclosure being for illustrative purposes only and forming no part of the claimed design; and,
FIG. 11 is is an additional top, front, and left side perspective view thereof, the broken-line disclosure being for illustrative purposes only and forming no part of the claimed design.