“Camp Evans, a decommissioned Army base in Wall Township, N.J., is frozen in midcentury, its brick administration buildings and boarded-up Quonset huts on hold from World War II. Fred Carl, 59, a former high school science teacher and the unofficial keeper of the site, leads a visitor to other throwbacks from that era: a collection of corrugated metal houses with porthole windows and conical roofs. They look like alien habitations dropped from the sky.