Keeping it simple...

This is a simple proof of concept, so in the name of simplicity, pre-soldered components are used when possible.

It will consist of an Adafruit Proto Tripler PiCowbell (for Pico and Pico W) as a baseplate and to easily add battery, power, and reset switches, duplicate sockets for each pin, and of course, mount the main boards. (It also comes in a Doubler variant)

Stacked on top is a Raspberry Pi RP2040 Pico with headers, paired with an Adafruit Picowbell Adalogger (providing the micro SD connector, and PCF8523 real-time clock with battery backup). Attached is also a large capacity LiPo (Lithium Polymer) battery.

There will be three "weatherproof" sensors connected through cable glands, and one breakout board version of a temperature sensor inside the waterproof container. 

• Two “weatherproof” DS18B20 temperature sensors will be connected to pins D13 and D14 using Stemma cables connected to DS18B20 chainable breakouts for their convenient screw terminals. 
• A weatherproof mesh enclosed SHT30 (temperature and relative-humidity) will connect via I2C. 
• An MCP9808 temperature sensor, which will be inside the container, will also connect via I2C using a Stemma QT cable (JST-SH 4-pin).

The circuit diagram looks like this, which is available on the Downloads page of this guide:
(Note that the SHT30 is represented with a Stemma QT version in this diagram)