I think the first suggestion would be the easier of the two.
They make strong, thick walled baloons don't they? . . . . .
I'll go and have a look at the furniture and have a think. I might have to make a frame fixed to the chassis. Perhaps I should get a new MOT first. Also I was in Jacksons of Old Arley recently and noticed that they now have lightweight refillable gas bottles, not SafeFill, another make which have attached tubes to refill from an outside filler cap. They weigh far less than a steel bottle which could be an advantage now I have a 100 litre fresh water tank. But but but they are unreasonably expensive. I like the idea of fitting the bottle I have already got, it would be lighter than two Calor bottles.