I have an '06 Explorer with a Class III hitch; weight carrying rating is 5000#; weight distribution rating is #7000. I am considering a Brenderup 2 horse trailer. Gross weight rating for this trailer is 5400#. Do I need a weight distribution hitch for this trailer? I'm thinking not, based on the trailer design, but would like opinions.

Because of the way Brenderup is designed, you don't need wdh for weight distributing and anit-sway, but since you are over 5000#'s you need it to be legal insurance wise as those numbers are the ones your insurance and police will use in an accident and you may get less coverage by breaking the truck manufactures hitch rating.

Not legal advice, but here goes:
Ford only "recommends" a WDH for trailers over 5000 pounds. GM does "require" a WDH in their trailer towing guide.

Since you have a Ford product you "May" be okay without a WDH.

Thank you both. If I go find a wdh, which one should I get for the Brenderup, which has surge brakes?

With as little as movement as it takes the coupler movement to activate the brakes, I think most chain wdh will work. But the only wdh that advertises they work with surge brakes is Equalizer. See my review and read the section about boats, http://mrtruck.net/wdh.htm