Hi Julynian
I think, and this would be well worth checking for your own safety, Flogas bottles for forklifts have an internal pick up pipe so as to be in the liquid and not in the vapour. If so, you will be delivering liquid to your regulator instead of vapour, not something I would want to be doing. The forktruck regulator is evidently a different animal as to a narrowboat type, so is the bottle conector. There is a non return valve on the hose that connects to the bottle, and the conectors are of an entirely different type than the normal boat and caravan type.
I will check my forktruck tomorrow, I know when the bottle is laid horizontal in its working position, there is an arrow on the under side which should point down, whenever a bottle has been changed without turning the bottle off liquid is always present.
Flogas do LPG with the normal connections but as you say there are not many places on the cut that do Flogas