Bonjour,
Heating a little boiler and install a water pump is to my opinion the most efficient way to save gas and autonomy and provide a good quantity of steam.
As I am a real fan of Stuart D10, my friend Max, great mecanics, offered me to build one and I asked him also to add a pump (I confirm, he is a real friend):
To join the machine to the pump, he realized at first a rigid sleeve which did not facilitate the alignment of the axes and generated a little effort on them.
To enhance this, he made what we call a "TOC" which allows a little tolerance between the two axes (see at 1'20"" ):
Just for the pleasure, in this video, you can guess the original Stuart D10 solution with its coupled pump. Of course, this solution can be adapted on any steam machine as soon as there is room enough to install a pump.