Ok, I’ve been a packaging engineer for over 45 years so I have a little insight on how things should ship?
PVC is the strongest but also the heaviest and most expensive.
Fiber tubes are what most use and are almost as strong as pvc.
Corrugated is strong enough as long as it is in a triangle shape and not square. If its square, it’ll fail for sure. Being triangle greatly increases its crush strength.
Also, the rod needs to be “suspended” (so to speak) so that it has the ability to flex some with heavy handling.
Best packaging I’ve seen is Dobyns rods.
Solid fiber tube, small piece of foam tubing on the rod tip, plastic sleeve secured around the rod and taped to the ends on the tube so it kinda free floats in the tube. Best I’ve seen.
When I ship a rod I will wrap bubble wrap around it in multiple places so it’s held in place ( but can still move if needed) with a generous amount at each end for tip and butt protection. Into a fiber tube ( I save mine) and ship it.