Get a box that is not too much bigger than an adult snake would be, line it with styrofoam/insulation. Place the snake in a pillow case, tie it well and pack it in the box w/crumpled up newspaper. Place a hand warmer thingy in a fluffy sock and put it in the box, not touching the snake. Actually, make sure the box is warm 1st, place the hand warmer in and let it heat up. Just make sure to keep the box closed as much as possible.
This is how I transport my Leo's and snakes, works really well.
Edit: I actually use the insulated boxes they were shipped in or the ones my rats come in. It is easy enough to whip one up though if you have to.
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