Good info provided......
So load up that Expedition 'camp ready'....you, full fuel tank, ALL passengers (Human & domesticated), stuff inside (backpacks, baggage, etc) and go to CAT Scales for weigh ticket.
It will give you weight on Front Axle, Rear Axle and total weight
Then you will have REAL numbers to work with
Subtract Total weight from that GCVWR (14,500#) that will give you an idea of trailer GVWR you can start looking at.
Subtract Rear Axle Weight from the RAWR (4128#) (FAWR 3150#)
What you left over is to be used to figure trailer tongue weight (10%-15% of trailers weight)
Also read your Expedition Owners Manual......pgs 239 thru 243
Has some good info about towing a trailer
2003 Expedition Owners ManualYou will need to install a 'brake controller'
Expedition is already set up with 4 & 7 pin connections back at receiver and has plug in connection under dash...just need the controller and harness
Tekonsha Prodigy P3 Brake ControllerCAT Scales