The problem areas are often under the clips where you can't see the corrosion. Brake lines are subject to same corrosion.

If line looks OK except for some surface rust, it may be hard to paint in a way that gives complete coverage. What I would do, is spray the lines with a rust treatment. Here in Canada, many of us have the cars rust treated annually, so those lines get sprayed anyway. But the same products are available in spray cans. Names here are Rust-Chek and Krown. You probably can't get those? If not, Fluid-Film should do a good job. I have used that inside rockers and other rust prone areas. https://www.fluid-film.com/

This is a lot easier than painting - just have to do it more often!

When I replaced fuel and brake lines on my old 300D, I did paint them while new with DOM-16 (similar to POR15)

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5