The doors are steel. My taxi signs are magnetic. The rear hatch is not steel as the magnetic UK sign needed when I travelled to France would not stick. The steel is very thin though. Oh and the bumpers are very flexible - I lost an argument with a truck and was pushed to the side of the road by him. Barely a scratch, no dents or warping in the rear bumper. Word of advice, never argue with a vehicle bigger than you!?!
i don't know.. i remember reading that the outer piece is aluminum with metal bracing behind it. i know my magnets didn't stick in certain spots.... and my scratches since 04 never did rust..... kick plates did rust though...