The ornamental design for a mount body for a solar panel, as shown and described.
FIG. 1 is a top front perspective view of a mount body for a solar panel showing our new design;
FIG. 2 is a top rear perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The broken lines shown represent unclaimed subject matter and form no part of the claimed design, including the disclaimed portion of the bottom of the mount body for a solar panel shown in FIG. 8.