Hi,
I also have a Edge with a tow package, and the curb weight is around 4,000 pounds. You will not exceed the 8400 GCVWR if the Edge weight is 4,900 pounds curb weight and you attach a 3,500 pound trailer to it with a 350 pound hitch weight.
So you can add about 900 pounds to the Edge in passengers and camping gear, then add 350 pounds of hitch weight, and tow a 3,500 pound trailer. The trailer GVWR can be up to about 4,200 pounds, as long as it's empty weight is less than 2,800. The empty weight + camping gear, food, pots and pans, water, propane, ect. should not exceed 3,500 pounds. That is the hitch weight rating. If you exceed 3500 by a few pounds, you will still be OK, and handling will not be adverse, but I would not go over say 3,600 pounds.
You can not use weight distribution equipment with the factory installed 1.25" square hitch receiver. Such a small trailer normally will not require it, and the Edge can handle 350 pounds of weight on the hitch without sinking and making the headlight point skyward.
Try looking at these brands.
http://www.scamptrailers.com/http://aliner.com/ IT really does take about 90 seconds to set this one up, and you will stay dry inside. Unlike a pop up trailer, if it is raining, you do not need to open this type up in a garage to dry them out to prevent mold in the canvas. The low center of gravity and low overall height while driving help in windy conditions, and improved fuel mileage over a standard height RV. Yes they are secure while set up for towing or camping.
Fred.