Tim, P38 is a fairly commonly used filler but if your model is definitely styrene then a dedicated plastic model filler such as Tamiya putty would adhere to the plastic that bit better as the putty solvent also dissolves the surface of the plastic.
Its also that bit more convenient as it comes ready to go in a tube rather than requiring to be mixed. I suspect it might not be as strong as a material so it depends really on the amount requiring to be filled.
Edited By Richard Simpson on 24/02/2023 19:48:30