Hello Jayne,
You should check the sizes of the bottles to ensure they will fit your caravan locker - dont just take dealers wod for it check a sample will actually fit.
Currently there are only a limited number of places where you can refil the new bottles, but the situation is continually changing, hopefully improving, - note you are not allowed to refill these bottle on garage forecourts, they are not insured for them so you must find a bottle filling agent.
Before making a booking for a site, it would be as well to check with B.P. or your supplier for locations near your destination where you can arrange refils.