Have you weighed the Keystone? Could be an overloaded condition causing the wear. If the axle is bent it could be bent back but,problem might return. 2003 might be covered under warrenty if it was not caused by overload or hitting something. If you hit something insurance might cover it.Contact Keystone and see if there have been any problems with this but ,don't hold your breath that they will admit it. Axle could have been installed wrong (bottom side up). A good spring shop should be able to repair this or a come-a-long and some tie downs with a tape measure might cure the problem but, new axle might be simpler.
If the tires aren't worn out yet take them to a tire shop and have them reversed on the rims and rebalanced. This way the deep tread will be on the inside where it is wearing. Shouldn't cost too much...maybe $20. This doesn't solve the problem but it will save you a little money.