Acetone would not be as severe an issue as MEK... Most commercial foamies are molded from a different type of foam than referenced as EPS/XPS (polystyrene) recognizable as Dow's Styrofoam. That may contribute to your specific foamies resistance to acetone.

Foam has come a long way with respect to its strength as the electric modelers have proven. Byron's foam was a more complex composite than that of EPS and XPS and was female vacuum molded. This produced a smooth surface texture which readily accepted Econokote with little to no issue back-in-the-day. They were strong enough to fly with only the Econokote film without having to be glassed.

I am enjoying your assembly process and look forward to more photos.