Or, you may find out, as I did, it isn't the axle at all. More often than not it's the spring hanger location. Factory specs, at least for my trailer, were allowed to be within 1/2" of diagonal measurement, while axle mounting specs need to be more like 1/8" or less. Pretty hard to get good axle alignment when the spring hangers are already that far out of square. Mine required cutting off and rewelding the hangers on one side to achieve alignment. Guy at the trailer shop said travel trailers are notorious for bad hanger location.