The answer is Yes, you need a WD hitch.
If you don't use a weight-distributing hitch, your vehicle is rated to tow 5000 pounds with a 500-pound max tongue weight. Your 2619 will weigh somewhere around 3200-3300 pounds when you are ready to hit the road, so you have a bit of margin there. However, the tongue weight will be 425-450 pounds, so you have almost no margin here. If you put stuff in the way-back of the Explorer, you will eat up this margin and more.
We have your exact vehicle, with a slightly heavier TM. By the time we load up the TM, and load up the way-back of the Explorer, there is quite a bit of rear-end squat. If uncorrected, this squat will cause all sorts of instability, since as the rear end squats, the front end rises. When weight is removed from the front wheels, steering and stability are changed - and the result is a very queasy feeling as you drive. Sudden or emergency maneuvers become quite dangerous.
My advice - don't risk it. Your tow vehicle and your TM - not to mention your life - are too valuable to risk for a couple hundred dollars.
BTW, if you haven't found it already (the site is hard to navigate), you might check the Ford website for this info and more. Go to
http://www.fleet.ford.com/truckbbas/...2/campercd.pdf
Bill