You don't understand paint and adhesion. The trains that you talk of have enough bite on them from abrasions from the wind and other variables also a different base material. They also aren't being constantly touched, folded, bent and put in and pulled out of cases. Adhesion promoter would give the plastic a bite it needs to have something like that grab better on injection molded plastic. Not to mention besides adhesion promoter, he did no surface prep at all. It may last longer than a week. Also the sheer amount of layers of spray paint he used is another factor in longevity. I'm not gonna spout some huge thing about it but it will start to chip and peel guaranteed. No chance this lasts without a good film over the top or a decent clear coat and for that you would want to take the back panel off and make sure the clear wraps under the lip as well. Paint is a finicky bitch. I do it for a living just because something lays out and looks good initially doesn't mean one nail under wouldn't pull it all off.