I agree, even at the hottest parts of the van, the engine and exhaust areas, that would not dry out a wet spot. If there was any drying effect at all, if would have to be in a pattern, not the entire shape of the van. So the van must have been there for a while, still if the rain was more than just a mist the area should also have still been wet. Very strange! Did you check the porch for a package?
