Hot water service for slideon camper

G'day Troopy.... Yes they do use a large amount of power on 12 volts, and are not for those who camp in one spot for a long time without 240v. It would not be practical to power them off 12v whilst camped without a generator. If you are usually on the move most days they work alright. I have one in our Piggyback trayback camper. I usually turn it on with an hour or two still left to travel when someone (usually the good wife!!!) wants a shower. You really need the vehicles alternator to do all the work. You'll get two short showers, or one long luxurious one.
A word of warning. Make sure you beef up the mounting system if you travel regularly on rough corrugated roads. At 15kg when full of water they need to be very well mounted. My first one was not, and broke away. Currently fitting another, fully bolted and braced mounts and extra strapping. Good luck with it. Timnivo.