I had a really good experience using polyethylene (PE) for the chest frame. I’ve really warmed up to that stuff. I went to a plastics shop today and they had a bunch of PE boxes. None was the perfect size for the Arduino Mega + protoshield, but there was a box that had dividers molded into it that was pretty damn close. So I bought one (PE is cheap!) and cut the dividers out with a flush-cutter. It closes, but it’s a little too snug with this particular protoshield on it. I’m going to build a new one that doesn’t use the pass-through headers, and will use lower-profile LEDs. Then it will fit with plenty of room. Getting power into there will still be a challenge, but I like the form factor. Smaller is better, since this has to mount on my belt.