I tried using Paper Mache on a test helmet and it warped REALLY badly.
If you try this, you have to get the Glue to Water ratio perfect; too much water and it'll warp, too much glue and I'm guessing something bad will happen but I'm not sure what
If you sucessfully do this, please upload the ratio you used; I'd be very interested in knowing it!
I used a 1:1 ratio, so maybe a 1:2 (Water:Glue) ratio? I'm not sure...