I'd be curious to hear what the people who replaced your axles and tires have to say about your current problem. I am not overly expert on the subject of trailer running gear and am assuming that your new axles were accurately installed, which is not always the case. (Perhaps the installation was even warranted.) Given that, I find it curious that you went from having inside wear on both sides to having outside wear on only one side.
I've done a bit of research and the following may help identify the problem.
Also, see "Dog Tracking" (below) if your trailer has conventional sprung axles. (FR does not mention that issue one way or the other but it looks from the Salem pictures on the Web as if you might.)
Two other thoughts, again assuming conventional (sprung) axles. Are the spring attachment points to the frame and axle properly positioned? Are any components worn from your previous problems?