fermentation heaters

Planning on building a keezer for cooling, and using a electric jacket for warming my 6 gal glass carboy. Now, where would I place the thermometer for when I'm using the jacket to warm?

 

Will the jacket cover the whole carboy? My fermwrap leaves a space and I tape the probe there.

 

I'm assuming it will leave some space. You trust how the thermometer taped on the side reads?

 

Yeah, works great. I cover the probe with a cut can cozy as insulation, and I do have a fermometer stuck to the carboy to see if there is consistency.