William, there is a choice of battery out there, and you will get various views on the best type, but, generally a Leisure type is better for caravanning as they are designed to cope with long steady discharge, unlike a normal car battery which is designed for heavy but short drain.
There are various types of Leisure battery, from the normal Lead/Acid type to the carbon fibre type, but prices reflect the difference in makeup.
You can pick up a lead/acid type for around