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If one pulls their mini-van manual and reads the fine print within their towing section, you'll most often find a statement like... Max 3,200 lbs towing condition is based on 150 lbs driver, no wind and no hills. In other words, perfect driving conditions. It might even have a 2nd sentence stating something like more passengers and/or cargo inside the vehicle, the LESS the vehicle can tow. In other words, if 500 lbs of passengers inside the Vehicle, then its xxxxx "gross weight aka: dry weight" attached trailer must weigh that same less amount. In other words, a vehicle with 500 lbs passengers + 3000 lbs trailer = 3,500 lbs weight (which is higher than 3,200 lbs number). Add additional stress of wind drag, hills and that 3,500 lbs number starts to feel like a trailer weighing 4,00-4,200 lbs (which is way over 3,200 lbs number). So in reality, 500 lbs passengers now has "max 2,700 lbs attached trailer" number.
If wondering, I have a V6 mini-van (with over sized engine) and sometimes tow a 2,600 "wet weight") 16.5' OB boat. I tow it on no hills, short distances and with wife + 2 kids in the vehicle. Nothing else inside the mini-van. Van pulls easy (with its extra large engine and in 3 gear) but I wouldn't want to pull more weight. Especially for long hauls, up/down hills and/or more stuff inside the vehicle.
Hope this helps in your mini-van towing research...