Squadron can't be beat for small gaps... if in fact it's a small gap you're filling... The Squadron putty is available in white(for over-painting light colors), and olive green(for camo and over-painting dark colors). It's sandable, blends great, and I've found it works very well when used in a few light applications. That's my experience. Unless you're building a micro...(if it already has styrene I doubt it's micro).. there's very little weight penalty. I can't think of a better putty. It works well with fiberglass, carbon fiber.. and of course styrene (ABS).. and a few other plastics and composites.