The pilot was landing a twin turboprop airplane on a gravel runway. A hill lies in the normal glide path to the runway, requiring a steeper than normal approach. The pilot said he misjudged the wind, and the rate of descent on final approach. He over rotated in the flare, and struck the tail, resulting in substantial damage to the lower aft fuselage. He indicated there were no preaccident mechanical anomalies with the airplane.