I don't know anything about the rain-x, but I would try the rain-x on some cheap scope before putting it on a good one. As far as covers, I have the blizzard brand pop-ups and they work fine as long as you get one that fits the scope perfect. If there a hair too small, the caps won't stay closed and if there too big they won't stay on good. I have a nikon 3x9x50 that I have a perfect fit on and they work great. In fact, I used them in the cold and rain this morning and they did not fog. However, I also have a leaupold var-I and I can't find one to the fit the eye piece correctly. the one I have is too small and won't stay closed. To sum it up, the blizzards are great if they fit.