>>1134321I'm pretty sure that already exists. The UP Steam Program always totes a car behind the 844 that treats the water before it is sent into the locomotive's boiler.
Also Norfolk Southern and Union Pacific owns quite an assortment of office special equipment, some of which are outfitted with HEP generators.
http://www.altoonaworks.info/pics/ocs.htmlhttps://www.up.com/aboutup/special_trains/historical_equipment/index.htm