Carrying a passenger helmet

[Badger]

I can get an entire (fairly substantial) backpack securely under my cargo net (I wasn't able to find a good laptop-friendly tailbag), and it also holds snug enough to keep a magazine flat and stationary.  I woudn't expect there would be trouble getting a helmet securely under there.  'Course...I got the expensive cargo net...$12 at the gear shop (I needed some way to get my hiking boots home after I acquired appropriate footwear).