Building the head base
First, after cutting the foam (with appropriate bevels), I preshaped it slightly with the heat gun, then edge glued the sub assemblies (there are 5 in the pattern for each side of the head, then glued those into the two halves, and finally glued the center seam joining the two halves.
After heat forming and sanding the edges, a slightly smoother skull for the inside of my fursuit head!