Our 16' pop top tows no differently at 80kph as 110kph. I feel a lot more comfortable keeping with the majority of traffic flow than being a rolling roadblock. I agree, if the van won't tow normally at 90kph then there's something amiss.
I may get howled down here but it's the same with those weight distribution hitches. If you need them, then once again, there's something not quite right with the van loading.
An interesting read:
Caravan Crashes - Here's Our Opinion | Clayton's Towing Services

