A lot depends on the powerplant. Is it electric, glow fuel or gasoline (petrol in the UK?)

Foam can be painted with latex (house paint type) however it is never "pretty". Also certain markers can be used if compatable with the foam. As noted covering with balsa would be an option if it doesn't add too much weight. Fiberglassing is also an option. Since the brands and availability of paint differ greatly check with a local supplier for suggestions and then test on a sample before using on your actual parts. Learn the difference between "dry' and "cured". Dry means the item can be handled. Cured means the finish has developed it's maximum hardness and resistance to solvents. Some finishes "dry" in a few minutes but can take weeks to "cure". Some containers will list this information where some don't.

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