I used to resort to carrying a pocketful of toilet paper to continually clean the condensation and snow or rain off my lenses. Then I went to flip-up covers which solved some of the problem, except for a bitter experience where they popped open in the brush in the rain, and I re-closed them on already wet lenses. Trapped moisture then fogged the scope even worse, losing me a fine bull after days of gut-busting hunting.
Now I use exclusively stretchable neoprene covers with instant release. They are made in Alaska. Try a google search for scopeshield neoprene or scopeshield alaska.