By Ju-min Park INCHEON, South Korea (Reuters) -From the muddy grounds of a former amusement park on South Korea's coast, tens of thousands of vehicles are being packed for shipment overseas as booming used car exports help to mitigate the impact of U.S. tariffs on new car sales. Soaked in sweat from the outdoor heat, workers are loading and strapping cars into containers around the clock for shipment from the makeshift facilities at South Korea's largest used car export hub in Incheon, west of Seoul. ...