Covered Hoppers Volume 2: Reporting Marks NAHX-XTRX: A Sampling of Privately-Owned Covered Hoppers 1961-1995 from Morning Sun Books is the first book in a two-book series loaded with color photographs and informative captions about covered hoppers in the diesel era. Photos feature covered hoppers owned by industries and other private owners. Whether as a reference for model building or for reminiscing about your favorite railroad's freight car fleet, Covered Hoppers Volume 2 has a place in your historical railroad library.