If you are running on Calour propane, Gastech do an adaptor that connects the propane tail directly on to a camping gaz cylinder. We take our own UK propane gas and the adaptor on the basis that if we run out of UK gas we can get hold of a camping gaz cylinder easily over in France. (They are available at most supermarkets). However in a max 3 week trip we haven't yet managed to run out of our UK gas.
We've gone electric on everything now except for the gas rings. On most sites its a fixed price for electricity so why not use it. As a result a 7 kilo calor lasted 2 months and we never had to use the camping gas standby. Camping Gas is also cheaper to buy in supermarkets abroad but its more expensive in the UK. So we decided to drop the calor and get another camping gas cylinder and save the weight of the calor bottle.
We take one full UK cylinder and one CampingGaz cylinder (both full of course, especially the UK one) and run off the CampingGaz, only using the UK cylinder during CampingGaz bottle replacement. This way you carry least weight and spend least amount of money without running out.