You don't need the 2500 Burb or Excursion to tow that lightweight trailer. If I was going with a larger trailer then yes the 2500 or X would be my first choice. The 1500 Burb will give you a more car like ride.
The compromises of non-towing ride/handling/power of the half tons from 10-15 years ago don't seem to make sense for the OP. They are taking long cross country trip, buy used, sell in 6 months. There is a huge difference in towing performance from that era in 3/4 tons with larger engines compared to half tons. Will a proeprly equipped half ton do it? Sure! But you'll be a lot happier towing 10k miles with an HD.
Fuel economy is the same for all gas engines. Might as well enjoy the extra power of a V10 or 8.1L.
Open up search to extended cab trucks. Ford calls is Supercab. You don't need crew cab and they are a premium.
