Whatever make of van you go for, if you know very little about caravans and their weak points I strongly suggest that prior to purchase you get an independent mobile engineers pre purchase inspection, use any of the NCC Approved Workshops mobile engineers.
Yes it will cost some money but could save you a lot more should you find problems after purchase.
If a seller is reluctant to allow an inspection, walk away,,,,,they are hiding something !!
Ask a very direct question, " Are there any faults or problems with the van "
Also, get whoever is selling the van to physically show you everything working, NEVER take a sellers word that everything is working ,,,,,quite often it is not.
If buying privately you want to see service records and damp reports , if buying from a dealer again service reports and damp reports are a must as well as what kind of warranty he will provide.
A caravan purchase is a business deal, not a love affair, be ruled by your head, not your heart !!!!!