Vinyl does not fade the way many people think. In many cases, what people call fading is really oxidation on the surface of the film. This can look brown, rusty, or dirty, especially when morning dew, moisture, and sun work together over time.
Heat by itself is not the main issue. Vinyl can handle high heat during proper installation, including post-heating. The bigger concern is moisture sitting on the surface, oxidation building up, and poor maintenance.