Aerosol conformal coating, either urethane or acrylic. The sensor circuit is a CMOS 555 oscillator plus a diode and lowpass filter to change the output to a DC level proportional to the oscillator frequency. By definition it is susceptible to changes in stray capacitance, so less is more. Mask off the sense area and connector with masking tape, lay down 2 or 3 layers of conformal coating, ***remove the tape*** (yes, not everyone does), and test.
Hot glue might work, but a) it is hot; b) it is thick. As it cools it might stress or even partially remove a component.
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