I used a cheapo bike bag from a mate. Think it was called World Bike Bag or something. A mate had the Evoc bag.
I wrapped my frame in all the bubble wrap and Corex I could lay my hands on. Removed the discs from the wheels. Used a separate wheel bag for the wheels.
They both did the job, but my bag was pretty hard work to roll along and carry on the train. So much so, that I found myself wishing there was a hire service for the Evoc bag.
Having said that, my mate has found some of the stitching on the inside of his Evoc starting to deteriorate. Should get fixed with little problem though. Wouldn’t get a cardboard box because of the hassle of transporting it on a train.