I read the How-to on painting the tail light covers with the spraypaint. But I've got a question: WHY? Why paint on the OUTSIDE of the plastic, where I'm going to wash and spray, and the sun will beat down, and road crap will scratch and take off paint?

Why not paint on the inside???

Has anyone tried painting on the inside? Beats getting overspray all over the car, or a limit the lifetime of the paint job?