I have been using a company called Shapeways to print my N scale models, and they not only offer printing services for individual designers, but in addition the general public can browse and purchase any items from their website (from various designers), make payment, and have the item printed on demand and shipped directly to them. Over the past several weeks I have been uploading test files, and have received multiple printed models. My 43' grain trailer was the first of a few designs that I have completed so far, and I am confident with the results to offer them to other interested N scale enthusiasts at this time.
A couple key points about 3D printing, is that it is somewhat expensive, and cost prohibitive in larger scales at the current time. As with all technology, this will likely change over time. In addition, the largest criticism that I have heard about 3D printing within the N scale community is the presence of surface texture, and lines from the "layering" of the model as the printer builds it up. I personally have seen some very slight variation in models due to the orientation as they were printed, meaning that one model may have been printed right side up, while another was printed standing on its end. This will cause variance between models due to the supporting material during printing.
In the end, there is a lot of great information on the internet regarding 3D printing. I am far from being an expert, and am simply taking advantage of a great technology that allows me to design and create N scale models from my home PC. I encourage you to find more about it if you haven't already.
My 43' grain trailer is now available for purchase through my Shapeways store. I am making it available as a single unit, or a pair, for a slightly better price than buying two separately. Look for more models being offered soon, and as I finish new designs.
Simply click on the following link and it will take you directly to my store: http://www.shapeways.com/shops/NScaleAddict
I look forward to seeing your own completed grain trailers and other models in the future. As always, please email me with any questions or feedback you may have.