Depends where it's going in your van. I made a cupboard big enough for 5kg but a smaller camping gaz would probably do.
Is it a new hob Is it a old hob Was there a bottle when you bought Besty? Most of the old school Hobs run on butane gas they are the normally blue. The other gas in orange bottles are propane gas. They throw-out more heat. But depends if the brass jets that attach to the hob are setup for it. 99% most likely will run on butane gas. Blue bottle. Hope that's some help?