I've built about 8 rockets in the past few months and I still feel like a beginner, but I still have not mastered filling in body tube spirals. I have used a substance called "Wonderfill," but either I'm not using it correctly or I'm not using it for the right purpose. When using it, I always see spirals in more places than I would expect with such a product. Again, it might be me and me alone. What do you use to fill spirals? Or do you use different things for different types of spirals?