I used a big gear bag that holds all my stuff: boots, riding suit and helmet. I put the helmet in a padded helmet bag and put it in the gear bag and it emerged without damage, both directions.
I bought the BMW Giant Bag or whatever it was called, and the helmet bag they sold.
It's pretty close to this one: https://www.revzilla.com/motorcycle/...sku_id=1125934
Helmet bag was kinda like this one: https://www.bobsbmw.com/store/produc...ort-helmet-bag