I have taken my mountain bike to London and back - in a box. I used a whole roll of duct tape, some bubble wrap - not loads. Bike was fine. In fact after my experience, I now trust a box more than a bag because a box gives rigidity but a bag doesn’t. I took the handle bar off, both wheels, and left it at that. I did wrap the rear derailleur in a fair amount of wrap because it was sitting directly on the floor of the box. Spacers were put between the brakes/pad thingies and a plastic thing on the fork (dunno what that is called either). The wheels sat either side of the bike, one at the fork end, one at the rear end. Have also flown two road bikes back to JHB after the Amashova, in boxes, and they are fine.