Blocking the bass mechanism, that's someone who isn't just guessing how to do it.
I've thought about making up boxes for shipping, and thought about using the extruded polystyrene insulation boards they sell at the big box hardware store, the way expanded polystyrene was used here. More resilient, and something about that EPS stuff squeaks bothers me a lot.
I wish I had a picture of how my Fratelli Crosio arrived from France, in its carrying bag, partly surrounded by a wad of something that looked like furniture stuffing, in a cardboard box that had become more of a bag at the end. Sturdy accordion, they don't make them like that any more.