Trackster

Like said, export directly from Sketchup as a stl.
Fix it with 3d Builder that is part of Windows10,
recheck in Netfabb if all holes are closed and
scale it in Meshlab >Filters>NormalsCurvatures Orientation>Transform Scale

Been doing it this way for a long time and maybe cumbersome, but it works for me. There are also beautiful plugins for Sketchup such as rounded corners and draw and extrude on curved surfaces. I still use the 2014 version and you get prompted to install a new version all the time, but then you need to reinstall all the plugins.

Looking good! Yes, there are complaints about the quality, but we need a new mindset here. These products are just a stand-in for the time being until new printers come out with better quality. Think of it as the dot matrix printers of 3d printing versus inkjet. When the time comes , one can simply throw out the old and substitute one of a better and cheaper quality . Most importantly , the design has already been done and can just be fed to any printer now or in the future. 

David, will there be any chance of scaling up the Kirow to 1/87 scale when ready? I don't mind cutting and modifying a bit . There was a kit available from a Dutch company, Kleinspoor, that I have wanted, but your's is a superior product. Congratulations!