Trailer weight and balance is a constant topic in the camper/RV forums.
Towing capacity is determined by both the vehicle's drive train and the physical trailer hitch configuration. In the Expedition's case the 9000-9200 pound max towing capacity requires an aftermarket weight distribution hitch AND the factory HD towing package which retails for about $300 on a new truck. HD engine and transmission radiators are the primary components and these can be retrofitted by a good mechanic (but probably not for 300 bucks). The round Bargman RV connector is an other key to the HD tow package, not just the 4-pole "boat trailer" connection. The 3.73 limited slip axles were part of the 2007 package. I think the ECU handles this on my 2017 as the axles are open. Working well so far as I only tow once or twice a month, not daily.
An indicator the WDH is set up properly is both the truck and trailer are level. Parallel to the road. Both the front rear suspensions of the truck should depress equally. If the rear drops an inch the front should too. Just measure to the top of the wheel arch before and after. If the front does not depress no weight transfer is taking place. Self leveling suspension must be switched Off during this process. Towing level i an indicator, not the goal. Self leveling suspensions or helper springs can make the truck level but don't transfer an once to the front axle. Helper springs to not change the axle rating either. Use a proper WDH. My personal recommendation is the dirt simple Equalizer (brand) in the appropriate weight range. Includes trail sway control (a topic all its own). Trailer sway is a euphemism for fishtailing, a very dangerous occurrence (note the previous video).
My Photobucket photos are being held for ransom by them so I can't post them anymore but for my under 6000 pound Rockwood Roo 23SS travel travel trailer using the Equalizer (brand) WDH the top of the ball with no trailer on it is 22-1/2" off the pavement. This was established buy long experimentation with my 2007 Expedition and the same draw-bar and trailer connected to my new 2017 had needed no changes. That's a good starting point if you have an Expedition but plan on an afternoon of adjustments. RV dealer was little help.
Final notes: Conventional trailers need 10% to 15% of their total weight on the ball. For my 6000 pound camper that's 600 pounds near the limit of the weight carrying capacity of the truck receiver. Boat trailers due to their weight distribution (heavy engine at the rear) need 8% to 10%. I have a tongue weight scale used for initial setup and when renting trailers. Also keep in mind that any weight put on the ball comes off the truck's weight carrying capacity. You shouldn't expect to tow 9200 pounds and carry seven passengers at the same time.
-- Chuck
