I'm getting really excited about this prop, so I thought I'd spill the beans sooner, rather than later.
I'm going to make a foam latex "skin" for one of my 3-axis skulls that is a reproduction of Jack Pierce and Boris Karloff's Frankenstein makeup.
At this stage, I'm beginning the initial sculpt in modeling clay over a Lindberg skull. Future steps involve making both a mold of the final sculpt and a duplicate of the skull in Ultracal (a type of plaster), filling the mold(s) with foam latex, baking the thing, hoping it comes out okay, and painting the final skin. If all goes well, it'll be like having Karloff the Uncanny in person!
Here's the sculpt so far. It's got a long way to go, but I'd say it's beginning to shape up pretty well.
It's sculpted around this skull as a base