Need Advice Painting Curtain Pan 31 Roadster

[Dollar Bill]

I searched the archives but couldn't find a previous thread on how to adequately preserve the recessed area of the curtain storage compartment. Due to limited access and clearance, spray painting is out of the question. Am thinking brush/roller as the only option but would like to hear how others have tackled this project.

Would love to know how they painted this area on the assembly line - Thinking it must have been dipped before assembly.