'Trim Insert', made of vinyl. Available in 2 widths: Wide (1") and Narrow (3/4").
I'm not a Sunrader owner, but I believe they use the Narrow insert. The insert isn't designed to be waterproof, just to cover and beautify the screws that hold the aluminum trim in place.
https://www.google.com/search?client=firefox-b-d&q=rv+trim+insert
There are other 'profiles' available but I don't remember anyone ever trying them and don't know if the would fit or offer any advantage.
https://www.automotiveauthorityllc.com/products/8-white-insert-trim-molding-flexible-screw-cover-rv-boat-camper?variant=33923685449
https://www.automotiveauthorityllc.com/products/white-rv-marine-vinyl-7-8-radius-insert-molding-flexible-screw-cover?variant=33984324041