I agree use some form of treatment like Eastwoods or POR15 or KFZ to treat the rust.

For best results grind it to bare metal and leave no visible rust behind - those sand paper on angle grinder discs - stripping discs are ideal for this.

Don't be scared to remove trim.

Make sure you follow the instructions on the tin! And then make sure you use an appropriate primer before you apply top coats

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!