If it were me, I would sand smooth and then primer and paint.
Rustoleum has a paint they formulate for plastic.
I've had good luck painting plastic.
A couple plastic parts on the brackets for my awning and such were dirty looking. I tried everything to clean.
Taped them off and painted them, they look like new now.
I paint my frame, A-frame and tongue area every year with a rattle can of spray paint.
2016 Toyota Tundra SR5, 5.7 V8