Well, seems like you narrowed it down to a misfire when wet issue. Spray(mist spray, not garden hose) some water (in the dark) on the engine, coil and area, wires, and see where the spark is coming from. Probably just a wire, but could be the coil pack. You'll be able to see it on the coil or wires, but may be less visible down by the plugs. I doubt it would be a low voltage wire problem if it only happens in the rain.