I called my insurers to be sure I was covered.
The rules and legalities are complicated. They are pretty much non-existant if you carry gas in a private sense, like a caravan owner would. But once you cross the line for commercial use it is different. There are limitations in a weight sense, off the top of my head you can carry up to 300 Kg without any necessary documentation or training.
But the vehicle you use should have appropriate ventialtion in addition to the gas being stored in a sealed container with a vent at its bottom which vents to the outside of the vehicle.
However I spoke to a number of gas supplier companies when I bought my L5 and recieved conflicting advise regarding some of the rules for transporting gas on the public highway commercially. I suggest anyone who goes hot-water does their own research.