What kind of fabric is it? My black slide toppers (Carefree SOK II model) is a black woven fabric of some type. I'm a big fan of Protect-All, but I can't imagine using any of their RV products on it. Maybe if the material was vinyl, but even then I'm not sure what PA product would work. It's not EPDM rubber, and it's not metal or fiberglass siding...
303 at least has a claim to be a fabric protector, so that would be my choice if I used anything. However, I never apply anything to my toppers.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL