I know it's a few months old this post, but how long is your caravan? Generally snaking accurs if your caravan is roughly the same dimensions as your towing vehicle, it's like a consetina effect, you should get a caravan specialist advise you if the caravan is suitable for the vehicle wheelbase you have. Also if snaking is bad I believe you can purchase dampers, like hydraulic suspension rods, to counter act the action.