The throngs filling campgrounds across America this weekend will include hardy outdoors types and those who prefer creature comforts, but they'll have at least one important thing in common: Nearly all of them are white. A small but committed group of campers is trying to change that by growing a generation of black campers, one person at a time. The National African-American RVers Association is composed almost exclusively of black people who camp, although it includes a few whites and Hispanics. The group doesn't have much money to buy ads or solicit new members. Instead, it always holds its major...