You can also do a "Site Search/Google" (blue task bar under log-in, "Search," and scroll to the last option).
I would be a little concerned about the high tongue weight
17Ds (typically over 400 pounds when loaded), as past Toyota products tended to be fairly softly sprung in the rear. I have read a lot about the use of WDH and airbags with previous Highlander generations. Perhaps the latest generation is different. I'll second Mike's suggestion to put 400+ pounds on the ball mount and see what happens. Measure at the front and rear wheel arches before and after to see how much the back goes down and how much the front goes up.
You also need to think about what you plan to carry in terms of passengers and cargo in the vehicle. My Pilot owner's manual includes a chart showing how maximum tongue weight
is reduced as you add people and/or equivalent cargo. The full rating assumes two people @150 pounds each with 30 pounds of cargo in the back. Exceeding the rear axle weight
rating can affect handling and accelerate wear on suspension and tires