Chris has made a good point concerning the CRIS document. In France, like in most other European countries, caravans are registered in the same way as cars. They have their own licence number and are required to have their own third party insurance (they're not covered by the car's insurance, as in the UK). Proof of registration is then automatically proof of insurance coverage. In such cases it will be only natural for the police to be cautious and ask for documentation for the caravan, too.