Never had mine come loose, but then I never used a torque wrench either. Hand tight + a little bit more by a wrench (nowhere near enough to strip) has always worked for me.
Keep in mind that the crush washer on plugs crushes - once - to seal. After that, you'll probably need a bit more torque to keep them snug in the head.
Keep in mind that the crush washer on plugs crushes - once - to seal. After that, you'll probably need a bit more torque to keep them snug in the head.