I don’t know about thin axles, but almost all of the axle tubes that are used for our RV’s are 2 3/8 OD with a 3/16 wall tube (small), and rated at 3500 lbs.…
Above 3500 lbs. up to 5200 lbs. will almost without exception be a 3inch tube with a 3/16” wall (larger)…
When you get into 6000 and 7000 lb. axles you may run into be 3inch tube with ¼” wall or larger OD tubes…
Of course there are smaller tubes for lighter axles that we don’t see too often especially on tandem axle trailers… however bent axles on RV trailers are not all that uncommon… the bend easily and are usually loaded to near the axle limits because of how the trailers are weight rated by reducing the tongue weight from the axle weights…
Hopefully you don’t have a problem getting it fixed but they may not automatically assume responsibility because of low mileage… the do bend easily and it can be caused by the road conditions, curbing, hitting CG tree roots, rocks or stumps, and other things… the axle could be positioned wrong instead of bent and create the same situation…
Good luck
