One thing that hasn't been addressed in these 10 pages that I could find was you saying that you were going to change the tires on the trailer.
I upgraded my trailer tires to the Kuhmo Radial 857 a few years back and I could IMMEDIATELY notice a significant improvement if the way my trailer tracked and handled the crosswinds routinely experienced in Texas, NM, CO and Wyoming. Don't know if they make them for your trailer's tire size.
Since you've going to great effort to make the F-150 tow this trailer, you really need to spend the extra money to upgrade the trailer tires as well.