You will see that the some of the information above is not quite correct, here is the instructions from the Ford 2013 manual:
When hooking-up a trailer using a weight-distributing hitch, always use
the following procedure:
1. Park the loaded vehicle, without the trailer, on a level surface.
2. Measure the height to the top of your vehicle’s front wheel opening
on the fender. This is H1.
3. Securely attach the loaded trailer to your vehicle without the
weight-distributing bars connected.
4. Measure the height to the top of your vehicle’s front wheel opening
on the fender a second time. This is H2.
5. Install and adjust the tension in the weight-distributing bars so that
the height of your vehicle’s front wheel opening on the fender is
approximately halfway between H1 and H2.
6. Check that the trailer is level or slightly nose down toward your
vehicle. If not, adjust the ball height accordingly and repeat
Steps 2–6.
Once the trailer is level or slightly nose down toward the vehicle:
• Lock the bar tension adjuster in place.
• Check that the trailer tongue securely attaches and locks onto the
hitch.
• Install safety chains, lighting, and trailer brake controls as required by
law or the trailer manufacturer.
I have found that after doing the adjustments above you might still want to add support such as air bags to level the van.