The only time I have experienced aggressive outside wear on the toad tires is when I forgot to unlock the steering.

Something you may look at is the side to side play in your tow bar/hitch setup. I have seen a couple of F150s that were actually slamming side to side while being towed. I stopped one of the drivers. He said he never felt it. There was a lot of play between the tow bar and the hitch receiver. Have someone follow you while you are towing to see if anything unusual is happening both on the straights

Can you post a pic of the tires?