Yes, propane would work, and may be the best way except when at home and compressed air is available, it could be that the propane option was for start ups when away from home.
All this was not an issue with steam cars that were commercially made back in the day; so far as I know all the small ones and even the large Stanley cars used a burner similar to what savarin suggests above:
"What about a primus burner, an alcohol flame heating some pipework then a hand pressurised kero or maybe the diesal tank that passes through the heated pipes and converted to a gas thats ignited to heat the boiler."
All that I have ever seen have used that type of burner, a pressure fed fuel supply, a vaporizer and a grid type burner plate; The small steam cars had limited tankage for water, and using it for a steam atomizing burner would have been wasteful.
The later steam cars, the Doble for instance used a gun type burner, pressure atomizing with a blower for draft, but they were worlds away in terms of size and sophistication and complexity.