Don't forget a deep lens hood to keep sprinkles off the glass. I occasionally use a giant zip-lock bag as a rain cover Just cut a corner out of the bag, slide it over the lens hood, and use a rubber band seal it. I sometimes leave a setup of this sort out in the pouring rain, with the Drebel machine-gunning frames.
IMO, if you're getting much rain, you at increased risk of getting zapped. With the smaller storms we get here in Az, CG lightning often (not always!) prefers the rain shaft area. Other safety tips include setting up in the vicinity of a tall object. (Don't get too close!) I feel reasonably safe standing not quite directly beneath lightning-protected power lines, at a point halfway between the nearest pair of poles. Most people killed or injured by lightning are not directly struck. They 'collect' a small fraction of stray current that 'spills' out from ground zero. A nearby strike can induce a high voltage gradient in the ground; hundreds, even thousands of volts per foot are possible. If your feet are apart, the current traveling through the ground may decide to go up one leg and down another. Stand with your feet touching whenever possible, and avoid grabbing anything unless necessary. I have a small rubber car-floor mat, with a piece of metal screen glued to the bottom, that I stand on whenever possible. Even when wet, this should isolate and insulate me fairly effectively.
