After much pulling of hair I finally managed to get the WS2812s running using the core of code from Just In Time Project Pages on the atmega328PB using the on-chip 8MHz oscillator with external 37kHz clock crystal.

With this version up and running I packaged it up in the spare sun-in-a-jar jar. I still need to drill a hole in the lid for the micro-usb socket, but that will have to wait till January.

The three boards soldered together and fitted into the housing (cut-outs needed because the tube is tapered)

Not particularly well finished

early (low light)

later (brighter, colours do not show up well in this)