Yes, there's definately a right- and wrong-way... and the right way takes a whole lot of effort. Everything I've ever painted on the interior has lasted great even still to this day... except the doors. They *will* require to be redone every 3~4x years if you do a good job. One of the things I liked in painting the skins black, was that it matched the black in the dash perfectly. Another thing I noticed is that your job looks blotchy; so either it was still wet (unlikely), or you didn't spray even/thin-layers.
Painting an interior can either be great or crap... but nothing in-between. - J
