The ornamental design for a caravan, as shown and described.
FIG. 1 is a top front right perspective view of a caravan showing our new design;
FIG. 2 is a top rear right perspective view thereof;
FIG. 3 is a top view thereof, shown without the unclaimed boat, for ease of illustration;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a front view thereof; and,
FIG. 7 is a rear view thereof.
The broken lines show portions of the caravan that form no part of the claimed design. The broken lines depicting a boat on the roof of the caravan shows environmental structure that forms no part of the claimed designs.