The ornamental design for an exteriorsurfaceconfiguration for a fuel tank, as shown and described.
FIG. 1 is a top perspective view of an exterior surface configuration for a fuel tank showing my new design.
FIG. 2 is a bottom perspective view thereof.
FIG. 3 is a front view thereof.
FIG. 4 is a rear view thereof.
FIG. 5 is a right side view thereof.
FIG. 6 is a left side view thereof.
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The even dash-dash broken lines in the drawings illustrate portions of the exterior surface configuration for a fuel tank that form no part of the claimed design.