It’s possible the roof of the caravan itself wasn’t in the prime of life; they do rot around the edges. Last winter, on a very windy day I was driving on the M1 motorway and pulled out to overtake a “well used” static caravan being transported by low loader. I was about fifty yards behind it when the entire aluminium roof of the caravan lifted off, blew across three lanes on our side, sailed over the central barrier and wrapped itself around the front end of a white van coming the opposite way.