fishing a heating cable

You have a fish tape that will reach the 2oo feet? I'm mildly surprised--my fish tape is only 50 feet long. Usually, what one does is tie some string to the fish tape, and then use the string to pull the cable through the space being fished.

Any ordinary electrical supply house should sell buckets of string, for exactly this purpose. Tape the string off on the end of the fish tape, and run the string through first. Then use the string to pull your cable run. If there is any possibility that you will pull cable through that run again, or just as a courtesy to anyone else who might pull a cable run through that space, you might attach some string to your cable, too, and tie it off at both ends (tape it to your cable, and then separate it when you have finished pulling your cable). That way, you or anyone else can pull cable without being obliged to fish the space again.