Since you are gettng wear on only one side of the tire I would expect that if you were to take the trailer to an alignment shop they would find the tow-in excessive. The axle
would need to be bent slightly for making the correction.
Since it is only one tire, I would also expect that if you were to weigh your trailer with a scale under each tire, the tire with the most wear would have the least weight
If you were to ask me "How do you know that?", my first response would be, "Because I know everything."
If you were to persist, I would tell you that the tire with the most weight
will dominate, the tire that is loaded less will skid a little, and wear.
I also know it is excessive toe-in and not excessive toe-out because the tire is worn on the outside edge. If it were excessive toe-out the wear would be on the inside edge.
P.S. I don't really know everything, and sometimes I get caught and stopped in my tracks. So catch me if you can.