I'm a Bondo advocate, and have been for many years. But I learned some years ago that just filling the surface spiral, the one in the glassine wrap, sometimes isn't enough to ensure a smooth final finish. Some tubes can have an even deeper spiral underneath the glassine (the one in the underlying Kraft paper wrap), and left unaddressed, over time it can expose itself in the final finish , perhaps due to changes in humidity, or perhaps due to the stress the tube takes from ejection pressure events. So with that last coat of paint one can have one's self thinking what a terrific finish on the model, only to have a spiral eventually appear over time, much to one's dismay.
So if I'm working on a scale model, for example, something that's expected to have no sign of spirals, I'll open up that underlying seam and fill it too. Yes, twice the spiral filling and sanding fun!
The photos below show a before and after. As was stated earlier in the thread, not all models necessarily warrant all that filling work. But for the ones that do, it's tough to ignore that second spiral.
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