You can't remove fade on any surface and bring it back to the original (before the stickers were placed there.) The outline pattern of the brighter color under the sticker area will always be noticeable. The only solutions are to repaint the entire surface so everything matches, or cover with a bigger sticker.
Sounds like your trailer skin is a "laminate"...
“laminate” – ... taking a resin plastic, reinforcing it (often with fiberglass) and then treating it with a gel-coat. The end result is then laminated onto a backer board and ultimately onto a superstructure of the RV-manufacturer’s choice.
https://rv-pro.com/features/great-debate-laminates-vs-stick-and-tin