Since the weight on the pate is most often incorrect I would suggest you either go to a weigh bridge with an empty van ie: no liquids or better still do it with full gas and water,plates, cutlery etc, bedding, mats, screens all the stuff that normally lives in the van, that will give you a true baseline to work from..............and while your at it weigh your tug as well as this combined weight can change how you load everything......sometimes you can't load your van to near max cap as the whole rig will be over.................Tug GCM minus tug weight plus tow ball weight, whats left of the Tug GCM is how much your van can weigh for you to tow, you should never be right on the limit though...........................