Just my opinion, but replacing the tire is not going to cure the problem. Found this info on "How to read tire wear" that may apply to your situation.
"Cups or scalloped dips appearing around the edge of the tread on one side or the other, almost always indicate worn (sometimes bent) suspension parts. Adjustment of wheel alignment alone will seldom cure the problem. Any worn component that connects the wheel to the car (ball joint, wheel bearing, shock absorber, springs, bushings, etc.) can cause this condition. Occasionally, wheels that are out of balance will wear like this, but wheel imbalance usually shows up as bald spots between the outside edges and center of the tread."
I realize the article says "car" but I think it also applies to a trailer. We had similar problems and had to replace axles and brackets.