End result first:
I still have to screw that controller box to the back of the shelf. It was salvaged from the previous IR remote controller. It now has ESP32 WLED inside.
Things learned:
Never buy 500mm lengths of Aluminium LED channel. Even if it is ridiculously cheap. Go for the 3m. Otherwise it is a PITA to install.
Take very careful note of which end is the start and end of the LED strip. I ended up installing mine the wrong way round and my data in line ended up being a little longer than I anticipated. Which brings me to…
If your LEDs are flickering like mad, install a ferrite choke on the data line close to the strip. Fixed mine right up.