Ocassionally, I have a coil which shorts to the solenoid tube and burns a hole through it. Insulation failure is usually down to either bad manufacturing, vibration, or to high temperature. Unusually it might be an impulse voltage but pretty rare on a  check valve coil. What are the coil operating parameters? Does it run especially hot? Is there a lot of vibration?Freeze-taw condition will give condensation in coil housing if not protected, air will always get in and condensate will form. Ex-coil with the whole coil protected in plastic casting might be a suggestion, and/or coil in heated cabinet or traced.
Also see too that nippels/boxes for cabels into coil housing either are of high quality (again ex nippels might do to ensure leakage tight) or again cast in cable with cable connection terminal in protected/warm area.
Always drip-nose on cable before entering solenoid.
Check that operating current and electrical protection is as should be under real operating conditions at site. Measure and observe!

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