I will just add this.
The other day I had to replace my third brake light, and used the golfgti.co.uk destructive removal method rather than replacing my spoiler. I had a chance to inspect the PCB used for the third brake light and was not impressed!
No conformal coat, crudely soldered in pins, and the PCB itself was cardboard-based, not fibre-based!
The PCB's I'm planning on producing will be significantly higher quality than that found in the third brake light. As I say (keep repeating myself, you guys must be getting sick of me) I intend on doing this properly and professionally. It's gonna be in my car as well and I want the highest quality for it.