Wellcome to the forum Bobby.
Hi, welcome here. Great step to buy a caravan. One that old must be checked for woodrot. I would suggest you take the van for a run over.
This sounds as a bargain that could become a big expense. Just make sure!!!!!!
You could take it to your nearest Camporld or caravan dealer. I understand that there is some kind of gadget nowadays that can detect the moist or woodrot.
A trained eye would also be of help.