Hi David,
if its just a few weeks, then should be ok left on the van, as it should be a leisure battery, which will charge back up from near on empty where as a car battery will not if it goes below about 8-9Volts, and you will charged it back up when you go away on your hols. If you are leaving it longer or over the winter months then i would remove it and store in the garage in a box to stop the cold getting to it. As the cold is one of the biggest killers of battery's
thats good Steve,
but most car & caravan battery's are replaced in and after the months of winter.
Also the older your batter becomes the more the cold will affect it