I bought mine in April 2012. No problems. Now, about the rust or corrosion. No matter how well I wrapped the lid to the woodbox on this smoker and on my Smokin-it, and no matter how well I lined the bottom of the smoker with foil and made sure it went up the sides, I always had great/drippings migrate beneath the foil. Some of the seasonings used in smoking can be rather corrosive for lack of a better term. Acidic? Sure. And combined with heat, and over time, they can etch metal, even stainless steel. However, I have not experienced any of that. Maybe it is in my future.
It is important to not confuse a great smoking patina with rust. Also, it is possible that the area that rusted could be a weld. Why? I don't know. Just a possibility. As for the wood box, let me ask the big question: do you get charcoal after a smoke or pure ash? Charcoal is indicative of no combustion. Ash means the wood caught fire. Fire is nothing more than oxidation, same as rust, but with a lot of heat. Combine that with whatever drips on or gets under the foil and you can expect deterioration.
And to you last question: No, you are doing nothing wrong. Just realize nothing lasts forever and that is why spare parts are available.