2012 Keystone Passport tire wear problem (with pics)....

It is normal for an axle to be bowed up in the center. It looks like you may have an excessive amount of bow, but that would cause the outer edge to wear more. Did someone place a jack under the axle center?

If you have a good level surface, and level the trailer perfectly, you can get a rough idea of wheel alignment by using a good level and a straight edge. A heavy duty truck service shop can do an alignment.