disappointment that a machine used as a tow vehicle is that the Prado's tow rating is pegged at 2500 kilograms for the long wheel base, yet the short wheel base Prado is 3000 kilograms. I know this is not answering your question just a reflection on the weight of your van.
Air suspension doesn't distribute the weight, so a WDH may be required. However the big question is whether Toyota recommend it for the Prado. Some manufacturers don't allow the extra stress of a WDH, some (like Jeep) recommend it. Do what the manufacturer says.
