Meat thermometer. Not to my NT. On the steering stem of the Goose. If you really wanted, just drill a small hole in one of the 'speaker' grills, add some double sided tape, and slip it in there.
Or, I saw the other day they now make USB cig lighter adapters that have a voltage readout as well as temp. So, install a 12v cig lighter outlet and plug one of those into it. Probably not waterproof. $10-$20
FWIW, I did try one of the inexpensive units for cars. One that had a clock, interior and exterior. LCD readout. The LCD was frequently 'blacked out' from being in direct sunlight. When it stopped working after a couple months I tossed it.