I did some research and it seems the Expedition may be able to do it. If you keep the tongue weight under the max of 920 you will satisfy the hitch rating. I could not find the payload #'s on the Expedition trailer tow guide
http://www.ford.com/resources/ford/general/pdf/towingguides/17RV&TT_Ford_Expedition_Sep7.pdf
But if they are similar to the F150 (1600-1800) with the same 3.5l Ecoboost (prolly less because of added features) and you can keep it under the payload numbers including your family and cargo plus having a properly set up WD hitch you may stay under all the ratings. I bought a tongue scale with my trailer to test my loads. Before my maiden voyage I pegged the scale. Those little items the family brings add up fast especially if they are placed in the front storage compartments.
I like you have heard the Armada is a good towing platform but I don't have any experience with them. I do occasionally borrow my FIL F150 Ecoboost to tow trailers when I don't have a truck and its a good platform to tow with.
I briefly towed a slightly heavier trailer with an older Navigator but I lightened the tongue weight by removing the heavy propane tanks off of the front and loading them inside the trailer slightly behind the axles. Something for a quick trip nothing that I would like to do on a regular basis.
When you look at the unloaded tongue weights don't get misled those 2 tanks filled plus battery add SUBSTANTIAL weight to the tongue of the trailer.
It's good that you are doing the research before it saves a lot of headaches later.
I also briefly had a E350 V10 passenger van and its hard to run out of space (I got 3 kids) or payload with those. Plenty of room and sitting up with legs down (more natural) made travelling less fatiguing for me. They were hard to find when I had mines. I only sold it because I need 4wd.
Good Luck!
