Hello Julie, welcome to the forum.
There are some things to bear in mind when buying a used caravan from a private vendor.
First and most importantly you need to satisfy yourself that the vendor has the right to sell the caravan.
All British built caravans manufactured after 1992 are registered under the
CRiS scheme
The vendor should be able to produce the necessary documents in
registered in their name to show that they are the legal owner.
A CRiS h.p.i. check costs