They will be shipped the same way if the Marvel graphic novel is anything to go by, those were also posted just in plastic bags.
I will say this though, I did get one of those Marvel books in a pretty beat up condition and they sent me a replacement free of charge.
This was a few years back but if they are still mailing them out the same one would hope they still have a policy to replace badly damaged items.
I do think there should be an option to pay like $1-2 for them to slip the books into a cardboard sleeve for extra protection (if they wouldnt do it free) though.