If you want a very easy method to integrate a temperature sensor with SmartThings, via a NodeMCU board, take a look at my ST_Anything project below.
You’ll need to determine what type of temperature sensor your smoker uses, or find a suitable replacement sensor capable of handling the temperature range. My project does support the Adafruit MAX31885 thermocouple which was added for a user wanting to monitor oven temperatures (although I haven’t tried compiling the class for that sensor in over a year, so it may need tweaks for use with a NodeMCU ESP8266 board. It was used with an Arduino originally.)