The answer is no, it will not be a problem. The reduced pressure in the hold at FL200 is equivalent to a descent under water of 3m. Completely negligible. Equally the temperature is a complete non issue. The operating range of these things is usually between -20 to +50c and they are tested way beyond that range. The coldest the hold could theoretically get is -54 but would be surprised that even unheated holds would get much below freezing. As far ice crystals forming and cracking anything, these things are usually tested to around 300atm or just short of 5,000 per square inch. No ice crystal is going to crack anything!!!
The pressure transducer used for dive computers is off a type that is too crude for effective ambient pressure monitoring above the surface on most dive computers. The transducers used on kit like the APD Evolution has more sensitive range as it is used to measure ambient pressure for calibration. But even that will have no effect.
All my kit goes in with my clothes etc and into the hold. So don't worry!