You can add up to 3 temperature sensors without sacrificing Watermark sensor inputs.
There is a standard pin reserved for a digital temperature sensor: pin 12.
This connects to the J12 connector (Also marked "DHT" on the PCB)
You can find the LoRaWAN code on Vinduino Github.
Replace this code:
On J13, there are two more digital pins available to connect temperature sensors.
Repeat above code, but then instead of pin 12, use the pin number the sensor is attached to.
The data line of the DS18B20 sensor needs a pull up resistor.