Mark
On the plus side, a 2006 Bailey will still be covered by the 6 year water ingress warranty, so the most important thing to check is that it has a fully stamped up service book. If possible ask for service invoices as well.
Ensure all the paperwork ties up with the van and using the CRIS number on the windows phone CRIS (their number should be on a sticker on one of the side windows) and ensure the caravan is not stolen or writen off etc.
Are you looking at a van that is at a dealer, or is it a private sale? From a dealer, you will have some comeback, but from a private seller, it is pretty well sold as seen.
I would recommend that if it is from a private seller that you phone a local mobile caravan service guy and ask him to come along with you. It could be money well spent.