Second batch:

To cover the USB port opening when not in use, I designed a compound cover, consisting of a 3-D printed part and a molded silicone plug. The picture below shows the 3-printed part on the left and the (also 3-D printed) mold for the silicone plug on the right next to it. I treated the inner side of the mold with an release agent, stuck the two parts together with a piece of tape and poured 2-component silicone into the mold.

Next I painted all the housing parts. I was using acrylic spray paint and a special primer for plastics. I had actually planned to paint the highlighted text on the case surfaces in a different colour with a very tiny brush to make the text more visible, but that was impossible given the porosity of the material, the low height and the fragility of some letters.