I found this wastebasket:
I'm gonna try it for the bucket. It will need to be cut to height and diameter, but I think it would make a strong, light, and flexible base for a helmet. I am thinking that it wouldn't need to be re-curved to the correct shape.
I have seen them at that Wal-something store and they have a slight grainy finish, but looks like it would hold paint without much difficulty. It costs $9 something at the store where I am.
just a thought...
It would at least match the trash can armor people are making.