Get the van on alevel piece of hard ground. Put all the corner steadies down and then ensure that the vanis level i.e. horizontal with the flat bit of concrete, tarmac or whatever.
Reverse the towing vehicle up as close as you can without touching the towing hitch. Most brackets on the tow vehicle will give you usually two bolts heights. If it is a Range Rover 'type' you may well have a geater choice.
Then bolt on the ball to the bracket at a height that is close to the visually good match. When the van is then loaded - heavyish to front, the weight will be distributed on the axle of the van with a leaning to the ball. Otherwise there will not be enough downward force on the ball and thus the bar to give a good gravity connection.
The key is to load properly and keep within the guide of 85% i.e. make sure the van is no more than 85% of the weight of the towing vehicle.
Big van towed by little mini = not good.
Stabiliser bars are advised.
Good luck.