Painting the smoke boxes.
Prevent 'over spray' around piping.
First, about an 1/8" wide masking tape is aligned with the back of the smoke box over the boiler jacket. Then a 1/4" wide is put over the previous tape for additional protection.
Then a 3rd layer is wrapped around the two 'running rails' to 'close up' the area.
The rest of the smoke box is taped off. A lot of work for such a small area!
The results are worth it, though!