You need to check the payload (cargo carrying capacity) on the Expy. You will run out of that, before you get close to towing a 9000 lb travel trailer.
Tow capacity is what Ford says your Expy could tow, if the driver weighed only 150 lbs, and had no cargo, or passengers. Ford also says there is a max weight rating on what the Expy can carry.
As you load people and cargo into (or on) the Expy, the tow rating and payload go down, pound for pound.
Loaded for camping, the Whitehawk trailer will weigh approximately 6500 lbs and requre about 900 lbs of available payload.
The Jay Flight will be about 800 lbs lighter and require about 700 lbs of payload.
Your payload number should be on the tire / loading sticker on your drivers door post. Find that number and subtract the weight of driver, passengers, and cargo. What ever is left over is payload available for trailer weight. You want some cushion here. Towing at max weight can be unpleasant, even on flatlands.