ALEXANDER, N.D. — It took little more than a day for 18-year-old Evan Jensen to smell opportunity in North Dakota’s booming oil patch. ....The mobile venture, called Better Showers, rolled into an RV campground in the heart of the oil patch in June. A shower costs $10, with a half-price discount for residents of the RV park where the business is located. Towels and washcloths are $1 extra. The water pressure is strong, the soap is free and there is no time limit. The business is parked along U.S. Highway 85, the busiest two-lane highway in western North Dakota, where...