Good plan. In their FAQ section, they address this issue (Faraday Cages). Below is the Q & A, but you are totally right to be concerned. Our SI's are much better sealed than other smokers and grills.
Q: Aren't BBQ grills, smokers, and ovens essentially "Faraday Cages" that would significantly reduce the wireless range of the MEATER probe?
In theory, a "Faraday Cage" will block RF signals from entering and exiting the cage. The good news is that BBQ grills, smokers, and ovens are not built or designed to be "Faraday Cages."
A good "Faraday Cage" has no gaps, slots, and holes; Are usually made of thick conductive material and designed with as little individual parts/pieces as possible (i.e. every joining edge or corner between materials are spot welded, etc.).
In reality BBQ grills, smokers, and ovens are anything but a "Faraday Cage." They have plenty of large air vents and gaps. If air and smoke can enter or exit your BBQ grill, smoker, and oven, then it'll be easy for 2.4GHz radio frequency to enter and exit through the same gaps and holes.
Also, there are a few MEATER backers in the comments section who did their own testing using a Bluetooth speaker to test the effect of their BBQ grill on Bluetooth signal range. They too have found that it made no noticeable difference