It just doesn't make sense to go with something even longer in the tooth than what you already have. Newest Excursions are 14 years old, and around here what few are still on the road are rusted out hulks that you'd never trust to tow anything heavy. Plus your choices of engine are either a diesel that the 8.1L would have no problem keeping up with, or the ticking time bomb 6.0's.
Short of getting an F350 and having a custom stretch done on the cab for a 3rd row, your only option for 3-row seating that can tow your trailer in something made in the last 10 years is a van.
How many years do you figure you have left with all 4 kids going camping? Sooner or later the oldest will decide it's not cool, and will rather spend the weekend at a friend's house. Then the five of you will fit in a crew cab truck.