We've been going back and forth between electric, wood-burning, and propane sauna heaters. They all have their pluses and minuses, but based on wanting true mobility for LBS, we narrowed it down to wood and propane. At the Design Review Committee meeting, the city would not accept our use of a wood-burning heater for multiple reasons; so propane it is! Though we are less familiar with them, the propane does resonate with other travel structures. Now on to researching options--there are fewer options on the market than electric or wood, but here is one from Scandia that seems common.
Here is a travel trailer with the propane tanks on the neck: