The Sioux City Explorers prepare for their tenth season in the Northern Baseball League when pre-season camp opens Friday. Benny Castillo returns as manager and says they concentrated on signing players with experienced veterans that’ve played in the majors and triple-A level.Castillo says the Explorers lost too many close games last season and will need to turn that around this year, and that’s why they’re concentrating on offense. Castillo says he likes the make-up of this team.The Explorers open camp on Friday and will play their first exhibition a day later.They will open the season at home on May 24th.