After much shopping and deliberation on form factor and case, I came to the conclusion that nothing I have is going to work.
My criteria are it has to be extremely waterproof, durable, small, readily available and cheap.
On the far right is what I have used for VERY rough prototypes, eg literally a plug in breadboard in a box. It is very durable and has served me well for various prototypes, but unfortunately it is way too big and otterbox no longer makes this sort of thing so it's not available either.
2nd from the right is the plano box I used last year. It is cheap ($5), it is extremely waterproof (why more cases don't copy the 3 latch design I don't know, it works great), but it lacks in durability and again, it is entirely too big.
Next is a plano case I thought was going to be the 2016 model, but it has a few big problems. The first is that it's not nearly as waterproof as the others. For some reason it has a vent hole that only gets plugged by the latch, and it's only rated down to 1 meter for 5 minutes. Second it's more expensive at $15, and finally it is still too big.
Finally is the otterbox 1000 on the left. It is about the perfect size on the exterior, but inside it is 1 mm too narrow to fit the pi zero width-wise, so fitting both the pi-zero and the 2 18650 batteries is going to be a mess.
I was working on the mount for the mast vane when it hit me, what is waterproof, tough, cheap, readily available and the right size? Pipe.
OK, it's not pretty, but it costs a whole $3 to make and I think it meets all of the criteria. (TBD, I will be water testing it once I get it glued up)
It's a tight squeeze to get the battery holder, the pi-zero, and the breakout all inside, but it fits. I will probably end up moving the antenna to the end.
The "stack" removed
The components (PiZero + usb port, male and female 40 pin connectors, breadboard, GPS, Accel/gyro/compass, battery holder and voltage regulator.
Bonus: I'm thinking about mounting this SSD1306 OLED display in a "window" on an end. I made this one by drilling a hole then filling it with epoxy. The results are not great. I ordered some casting resin, hopefully that will yield better clarity.
If all goes well, I should have the new prototype functioning in the next week or so and ready for some winter testing (aka driving around with it in the car, maybe if we get another cold snap it will make it out on the iceboat)