I agree... forget the towing capacity and concentrate on the SUV's payload capacity as that will be your limiting factor. ANYTHING you put in or on the SUV will have to be subtracted from the payload rating. Once you have that weight figured out, the tongue weight of the trailer can NOT exceed that remaining payload capacity.
The best way to figure the tongue weight (other than getting it actually weighed) is to take the GVWR of the trailer and multiply it by at least 12%. For example... if the trailer's gross weight is say 8000 lbs, then the tongue weight will be around 960 lbs. If your SUV has a 1500 lb payload capacity and you put another 500 lbs of people, equipment, other stuff....you've just maxed out the payload capacity of the SUV.
Hope this helps
Ron