I agree that is a pretty heavy trailer. Look at the "dry" weight and add about 1500 lb to it. Unless you are in a toy hauler, that's about as much as most normal travellers would ever add to a trailer. You may be thinking you have to be able to carry the gross weight rating.
The gross weight rating is generally the combined capability of the axles, no necessarily what you would realistically put in it.
ETA: The weights the dealer shows don't even add up right. Ask the dealer to verify them by the actual sticker on the RV.
Most people add 1000-1200 lb to the dry weight, unless you are a compulsive packer who takes EVERYTHING.
Get the correct dry weight, add about 1200 to it. Check that against the capacities of the Expedition. Google "Expedition trailer towing selector" for the year you are interested in. You will get the numbers straight from Ford, without a lot of guesswork from people who haven't bothered checking. An Expedition with the 3.5L Ecoboost engine, max towing package, and 3.73 axle is rated at 9200 lb. The Ecoboost is a towing beast.