Help needed, sunroof filling

Hi, I am looking for advice on how to remove a sunroof from a model, I have a diecast 1/24 MK2 Astra model that I'd like to build as a rally car so the sunroof must go, but how? I am concerned that to use styrene and filler it will crack? Has anyone any experience/advice please?
thanks

just cut sheet medal to fit and bond together