I think it's mk 4. I've been working on this for years with many revisions. In the summer I sorted the power issues with a bigger solar panel and battery.
I was using a envirophat but I broke the analog converter, seems they don't like 12v. Whoops. So I grabbed some bits from the other revisions of my weather system and created my own envirophat :)
Now all the wind and rain sensors are wired in and setup it's just the code to do over with xmas break. I should be studying for my OU degree but this is more fun. ;)
It's running a pi zero, BMP280, SI1145, TSL2561 and a MCP3008 for the wind direction as that uses a resister ladder for the 8 directions.
The power is from a 12v to 5v converter from eBay that is waterproof. Meant for cars. One of these.
Should mean I don't have to worry about voltage drop from the solar panel controller to the Pi as the 12v to 5v is on the back of the case. I tested it with my bench supply and it maintains a nice 5v output with a big range of voltages. My solar panel controller outputs 12v. (well about 13v if on the battery).
This is the case, just about enough room. Had to solder the wifi to the zero to get it to fit.