DULUTH, MN (AP) -- It's been a month since Travis Kladivo last rode a kite tube. And doctors say the 20-year-old's body has almost healed. On June 25, Kladivo, whose family owns a resort on Lake Vermilion, joined a growing number of thrill-seekers seriously injured while riding a kite tube, a huge, inflatable toy designed to float in the air with a rider aboard. The day after Kladivo's accident, a 42-year-old man was killed in a kite tube accident on Little St. Germain Lake in Wisconsin. Since then, the bestselling version of the device, the Sportsstuff Inc.-brand Wego kite tube,...