In my limited experience, scraping off paint never works the way I want it to. I'd probably suggest using rubber cement, mustard, or tape to mask off the areas you want to look damaged and weathered. Then, just remove it, and there you go! The gray Sintra might work in this case, but I'd probably suggest using an aluminum paint as a base color to give it more of a metallic look. If you do use an aluminum or metallic paint as your base color, then any color of Sintra should work, including white. Hope that helps!