Maybe but there is the undeniable fact that you are experiencing uneven tire wear. The upper limits in Toe In adjustment rest around 1/8". How does it drive, are you experiencing any drifting? There are other factors that could influence tire wear, like uneven load distribution along the axle where one tire is more loaded than the other or a bent axle spline, or excessive and uneven camber. We do not know how that axle came to be 3/8" off in one side but a hard thump on the road or a ramp could have force it back and bent the spline. Before you move the axle either one side forward or the other backwards make sure to the best of your capabilities that nothing is bent in the axle or suspension, and that the wheels are vertically straight (camber) that the top of the wheel is not either leaning to the inside or to the outside too much. As for "toe in" the front of the tires are the they pointing in or out? Sometimes if there are no problems on how the trailer drives and as long as the uneven tire wear is not too excessive sometimes it can be cheaper to replace a tire here and there than to replace an axle or chase some load factor or alignment problem. In some trailers it is easy to move the axle in others welding may be involved and be more complicated. You would have to make that call to move it or not.