@Silver Steve,

If you are buying your own designs, use the HP Multi Jet Fusion Printer. It is listed as HP Nylon at the bottom of the model upload page.
Capture 024.png

It is about the same price as Premium Black or White, but it is stronger and has an eggshell finish. I think I had to tweak a few thicknesses on the Wahoo mount so that Shapeways didn't automatically reject the model for wall thickness.

Unfortunately, this is still a Makers Only material, but as soon as it goes public I will disable the Premium Black and White and replace it with the Gray and Black HP Nylon parts in my listings.

Also a suggestion on that model, make your GoPro section a bit shorter, space permitting.