When I bought my first caravan it was wasn't registered to the current owner or to the address where I collected it from although I was happy the person selling it actually lived at that address. When I asked about the CRIS document he gave me a blank stare as he had never heard of it and claimed that when he bought the 'van from a dealer, they hadn't mentioned it. He did supply the receipt from the dealer and I checked with CRIS but all they would confirm was that the 'van wasn't reported as stolen or as an insurance write-off. They wouldn't tell me who it was registered to so I could check myself that it wasn't stolen. Effectively that broke the chain as I couldn't register the van in my name without the document.
Whilst in my ownership it was stopped by the police in a routine caravan check and once again checked and was found to not be reported as stolen.
It was a super caravan and I was very glad I decided to buy it, selling it a few years later for nealy as much as I paid for it.
Don't dismiss a caravan out of hand if the seller can't supply the CRIS document BUT be very carefull. The buyer of my van was happy as I supplied photo's of me, my car and van at various sites over a number of years. At least he knew the van wasn't recently stolen.