The most important first question is ... is your Expedition rated to carry this weight on the bumper (with your already loaded cargo)? Go back to Ford and get the correct bumper mount towing specs as it applies to your specific vehicle. Then adjust hitch capacity based upon the cargo you will pre-load into the vehicle (fuel, yourself, bride, kids, pets, food, bikes, beer, mother in law, etc).
And remember, a WDH can be quite heavy - just by itself (mine added 45 pounds to the hitch).
I don't know any of your specs - but it is a common occurrence to overload things because various salesmen state it's OK? Their job is not to educate you but rather sell you something!
Ultimately if you are overloaded then a WDH won't perform magic and make things right.
Now for some more ignorance on my part ... is a Keystone Hideout a true Heartland product? Regardless if it is (or not), enjoy the lifestyle.