This Is what I do and works well:
1. Shape your foam PU is good
2. add some fiberglass with polyesterresin on top
3. let it cure
4. Sand it of rough edges
5. add boddy filler polyesterbased if you used polyester with fiberglass, epoxybased if you used epoxy with fiberglass
6. repeat step 4 and 5 till perfect smooth surface
7. Paint with a 2K spraycan
8. Sand it a bit to remove "orange peel"
9. Polish it
10. Enjoy your work and have a beer...