Roof Deicing on Metal Roofs

I have to install heat trace on a metal roof. On some of the manufactures websites, I got the idea that you can't use regular de icing cable on metal roofs. What should I use? Any installation pointers? Are there any diagrams showing the best way to install the cable on metal roofs? There is a dormer roof away from the bottom edge of the roof and a number of valleys.

Thanks