Drip rail chrome molding install

[DrPhilgood]

I have a 67 coupe that Im trying to install new chrome molding on the drip rails but it wont snap on. I can get one part on and then as I move down the chrome, the part that already snapped on, snaps off again. Is there a secret to it? Should I sand down the paint off the rail before trying to snap it on?

For those of you who have helped me with previous threads, thanks. Im getting this done one step at a time with all your help.