2005 Rockwood Roo 232. Tires wear uneven. Torsion Axle Bad?

If both tires have the inside tread worn down, it sounds you've been putting too much weight in the trailer. This will force the axle's camber down and splay out the wheels.

Or perhaps the axle has permanently lost its camber?

Not sure about your Roo, but some manufacturer's install under-weight axles that are really not up to the job.