Hi Jo,
Like most backpacks, the Luzon is water resistant, but not waterproof. When I referred to a rain shell, I was actually talking about a jacket, not a pack cover. That said, I don’t recommend pack covers anyway because they don’t work well in heavy rain. It’s best to protect the contents of your pack on the inside with a dry sack or plastic bags. That will give you a fully waterproof system. I recommend my favorite dry sacks on the "Top Picks" page of my Gear Guide. You can find that through by clicking the "Gear Guide" tab in the menu bar at the top of any page on my site. Hope that helps!