This was the case some years back, as the caravans all used the same simple lock from the same manufacturer with spare keys available from any dealer. It was fairly common for people on site who mislaid their key to see if anyone else had the same one. I do not believe there was a single key to pen all f them but if I remember correctly there was possibly about thirty in the set.I once read that most caravan dealers have one key which fits all the caravans of a particular make and perhaps other makes which use the same lock manufacturer and that one caravan dealer had his (called Key to Pass) stolen, which meant that the thief had a key which would open every caravan of that make in the UK.
The caravans on sale now no longer have this problem, as the keys are mostly individual to the caravan.