I am in your situation regarding life casting, and I mentioned latex to be used to make things like wrinkles or protrusions of the face to be stuck onto a mask. For some reason, the mask i pictured was more of a wrinkly structure than the pictured one.
Anyway, I think if you can make a mask from pepakura, and make it slightly larger than your head, you might be able to fit your head inside it. Ofcourse, it may make you look like a bobble head, but other than that, I see no method to use epoxy resin to make a tightly fitting mask, other than to make it in 2 parts, such as a face part and a back of the head part with the seam running vertically just in front of the ears.