LAST spring, Bob Ripka decided the time had come for drastic change. His once-robust income from his job at a printing company was dwindling. His family lost its house in the real estate crash. And employment prospects around his home in Pine City, Minn., more than an hour north of Minneapolis, appeared scant. He heard talk around town about plentiful work in North Dakota, where new drilling technologies are driving an oil boom. “And I decided, ‘Well, I’m going to go make some money,’ ” he recalled in an interview. So on Memorial Day weekend, Mr. Ripka, 48, removed the rear seats from his 2003 Dodge minivan and ... (full story)