If the thermometers are able to read high enough temps without breaking you could always test all 3 by seeing what they read on boiling water - 212F? That's how we test probes for food at work anyway!

I'd also suggest having the stat prob inside a tub - with mine I melted a hole *just* big enough for it to fit thru, then taped up either side to stop it falling out / messing with humidity.