Before I try and answer Carl’s question, I should say I have taken the bait and tried to work out which RKO 1937 movie the scale model pictured above is from and what it represents. @T.Albers if you have worked on things of this kind you have some (more) serious modeling experience (than I do).
RKO made numerous interwar films that fall into the genre of “preparedness” movies, as in, “We’re not in the war yet, but . . .” The 1937 film that I think fits the bill is “Sea Devils” which is actually a Coast Guard film. This screen grab shows the model, which is of a cutter that might have been named “Taro” (the movie dialogue I have heard is indistinct):
Plus there’s this highly melodramatic YouTube clip “Distress Call” in which the cutter goes to the rescue of the burning S.S. Paradise, which is having a Titanic experience:
Back to the filler. I used lightweight/balsa aircraft filler a long time ago while building car models. Unlike the styrene fillers of the time, which dried rock hard/inflexible and had a tendency to crack, balsa filler was light and sanded into contours easily. These products tend to be discussed only on balsa plane model forums. They are still used by RC aircraft modelers, some of whom actually recommend Elmer’s light wood filler and ordinary spackling paste as an alternative.
That suggestion makes sense because if you are only filling very small spaces between metal and a plastic infill that is flush with the metal surface, you do not need a filler that is going to produce a noticeable edge where it meets the plastic surface. Nor do you need to cover that whole surface to make the painted insert appear to be a continuation of the metal surrounding it. I have used Alclad grey micro-filler to prime plastic parts that need as near as possible a perfect finish i.e. if a simulated metal finish is going to be applied over them. Fortunately ordinary acrylic paint finishes are a lot more forgiving.
