If you want more accuracy than that (I doubt it's necessary, but that's your business), you'd need a stainless steel "thermowell" which extends into the fermenter and hold the thermometer or ranco probe.
Or you could make a ghetto version by drilling a plastic bucket for a stopper, then drilling the stopper with a hole just barely big enough to shove the probe of a thermometer in.
But I'd think this could be a sanitation concern.
Bottle conditioning: Robust Porter
Drinking: Saison Dupont clone, tripel
Coming soon: Columbus APA, Rich Red ale