You could always cheat and paint onto a decal then cut it to a fixed width.
I have paint problems since I have eye and hand problems.
So do I but it's practice and patience. You paint from the wrist, elbow and shoulder. The whole arm, not the hand.
There are blind people who do calligraphy because it's practiced brush strokes the whole arm in certain patterns.
Yellow wavy stripes are easy, try hussar braid.
OMG! HUSSAR BRAID, on their Dolmans, Pelisses, Shakoes and Busbies!!! Now THERE's a test for patience if one wants to do it properly! I've done it, and it's exactly as Steve says- wrist, elbow and shoulder, not the hand/fingers- Practice on a junker. And try it sometime with the Golds and Silvers of the braid on the Officers' varieties!!! I LOVE the Napoleonics- such a beautiful variety of color and flamboyance...
To be accurate, one paints the Yellow bands on the vehicle by hand; one can also cheat by airbrushing the Yellow on in the areas where it's required, and MASKING the Yellow with Kabuki tape after it's dried properly, (at least 48 hours drying time), then airbrushing some more Yellow over the masking tape to prevent your camo colors from bleeding in under the masking tape. Once that has dried, airbrush your camo colors onto your subject. Remove your masking tape after the whole shebang has dried and, PRESTO! Japanese-style Yellow Bands!!!
Hope this helps!