I made a Pepakura model of this Uruk helmet but finally got around to finishing it.
I used Smooth-On Roto to build up the helmet walls by slush casting on the inside. I then applied Bondo to the outside to smooth out the geometry. Fortunately, I didn't have to sand too much to bring it into spec with Orcish craftsmanship!
I Pepped the back plate but in the end it was just easier to heat form some 1/8" styrene.
The final pics!
Lots more detail and WIP pics on my blog!