To add the raised details I first drew them on paper and sized everything against the helmet itself. Then I cut it out and traced the patterns onto craft foam and hot glued it onto the helmet. I then sealed the foam with wood glue and used joint filler to fill in the gaps where the foam pieces met and sanded it smooth. At this point you can prime your helmet once more to see if there are any imperfections to sand out.
This would be a good time to add the hardware for the helmet to open. I used the smallest hinge for a cabinet I could find from the hardware store. Just add it at the very top of the helmet where the two pieces will meet and follow the instructions that come with the hinge to install it.
I also used two clasp closures on both sides of the bottom of the helmet to keep it closed tightly.