The ornamental design for the base for outrigger mount, as shown and described.
FIG. 1 is a first perspective view of an embodiment of a base of an outrigger mount;
FIG. 2 is a second perspective view of the base of the outrigger mount;
FIG. 3 is a third perspective view of the base of the outrigger mount;
FIG. 4 is a fourth perspective view of the base of the outrigger mount;
FIG. 5 is a rear view of the base of the outrigger mount;
FIG. 6 is a front view of the base of the outrigger mount;
FIG. 7 is first side view of the base of the outrigger mount;
FIG. 8 is a second side view of the base of the outrigger mount;
FIG. 9 is a top view of the base of the outrigger mount; and,
FIG. 10 is a bottom view of the base of the outrigger mount.
Any components in the appended drawings shown in broken lines are for illustrative purposes only and form no part of the claimed design or a specified embodiment thereof.