Because it's animal-based, use unbuffered mount & mat boards in the frame.
I suggest sewing the snake skin to a pH-neutral, unbuffered mount board, using cotton thread. The needle holes will be permanent, but small enough that they shouldn't show.
You could also sew the snake skin to an inert fabric & stretch it over stretcher bars.
Above all, don't use any kind of adhesive on the skin. There is no easy way to mount something like this, but needle & thread is the best way, as far as I know.
After mounting, how about putting the skin in a UV-filtering acrylic box-frame?
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Jim Miller,holder of CPFcm designation; FACTS/GAFP Committee Member