Unless you're guaranteed access to electricity along the way, meaning you'd have an electric water heater as well as using electricity for bits of cooking and interior heating, you'll have a propane tank taking up some space. And how much space is reserved for a water tank is another issue.
You can reduce the size of the water holding tank you carry with you if you take a tankless or on demand water heater. This is because it turns on the heat only as the taps are turned on and the water begins flowing.
So you can hook up to pipes at a camp and heat the water on demand, rather than having to keep a certain amount of heated water at the ready. And if you go with this type of RV water heater, it means you'll also save on energy.
A tankless RV water heater can be both an energy saver and a space saver. Not only would you save on the space normally taken up by a sizable water tank, but a tankless heater is an energy efficient hot water heater.
You gas or other energy supply would extend a bit longer, since you wouldn't be using energy to heat water you weren't using, and you wouldn't be losing heat energy from the unused water either.
A tankless system could work very well in an RV, where energy and space saving are paramount.
To read more A Tankless RV Water Heater In Restricted Spaces
