What if the snake strikes or yawns and gets it's teeth stuck in the plastic bag? What about the heat from the heat tape above? I personally would not use plastic bags and tape. Never say the snake is to big to get out. I saw one episode on Animal Planet where this pretty big Reticulated Python squeezed into a crack and the guy could not get his arm into.

What about the plastic sheets used in drop ceilings to cover the lights? They are corrugated pretty thin and can with stand some heat. You could also install it with hot glue.