Neither, springs or axle.

If a tire is over inflated, it will wear in the middle. If its under inflated it will wear on the edges-both edges.

Given the age of your trailer, id have the axle and springs checked. And now would be a good time to make sure your spare is properly inflated, your lug wrench is in the truck AND fits your lugs and that your jack is there and that you have a flashlight and the batteries are good. I. It will happen.

Wannabe...