Ah, okay. I get what you mean.
What I did was to use two UV different maps for the fuselage / wings object. There’s one that’s unwrapped in the normal way to get a fairly even UV map all around which I used for the grungy textures. I then added a separate UV map where I selected the right half of the fuselage, went into orthographic view, selected (for example) right side view and in the UV unwrap menu selected ‘project from view’. I then did the same with the other side, the top and bottom views, selecting only the bits of the mesh that you want to appear in each UV island before each unwrap. I then arranged them so they didn’t overlap and exported the UV map to Inkscape to do the colours. This is the UV map I ended up with using this technique:
The diffuse colour map then looked like this:
…and, because it’s symmetrical I just needed to do most of the lines once and mirror them (though not the text, obviously). Then a bit of tweaking of the lines back in Inkscape once I’ve seen them on the model to make sure they’re in the right place (making sure you’ve applied the texture to the second UV map, of course). It’s quite mechanical and using curves in Inkscape so it sounds similar to what you’re used to.
Does that help?