I agree. You should prime first. And try washing the surface with soapy water. There could be mold-release agents still on the plastic that hampers the application of paint. That should make the white "stick" better.
Unfortunately, that may not solve the problem of brush marks. To get really white results youll need several coats, which will leave you with brush marks. Maybe you should try an airbrush.
Btw, isnt the interior of an F-16 supposed to be gray, not white?