I think you'd want to keep the shrink tubing away from hot parts. I've burned enough heat shrink with a match not to want to inhale that stuff in my pv. I used it all the time in my job to prevent contact with adjacent wiring and ground.
If you think about it, the center of the coil gets hot enough to glow cherry red. The leads are also nichrome wire and don't heat up as much because they are in contact with the bowl and
juice in it. They are still hot, just below the glow level. I've had one battery fail because of a failed solder joint inside the battery. That part can get warm, also, but I think that the failure was probably a cold joint at the factory.