I have been present a few times when caravans rocked.
On one occasion the host had not put the stabilising legs down properly or something miscarried and, with the party in full swing, the caravan suddenly tipped onto one end with a tangle of bodies, arms and legs ending up in a heap leavened with cocktail sausages, beer, wine and cider, and one couple falling through the open window at the end.
A maximum advisable number of adults inside a caravan at any one time would seem to be about three per metre of caravan length.
This assumes that not more than five percent of those present is clinically obese and that everyone knows each other fairly well, or would like to, that all are agile enough to climb over others when required and about half those present are prepared to spend the evening standing up (when not actually falling down).
It also assumes that those present who might wish to mate do so somewhere outside, if only to avoid taking up too much space which could be used for standing glasses and bottles on.
This probably contravenes health and safety, fire regulations, at least a few by-laws and possibly the criminal code almost anywhere in the world, but what decent party doesn't?