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You may not have noticed this before but in the Ship Designer of Galactic Civilizations III you can take the ships you have designed (or downloaded) and export them as a .OBJ file.  This can be used by 3D printers but also on a cool site called Sketchfab.  It's super easy to set up.

Here are a couple I've already uploaded:

 Have fun!

p.s. Bonus one:

https://skfb.ly/6tIOy