Advice... Two words... LENS CAPS!
Nothing will keep your view clean, dry, distortion free, etc if you let rain hit your lenses all day. Keep your lenses dry with some lens caps and at least you won't be fighting water droplets.
Fog? You shouldn't have any fog or moisture on the INSIDE of your scope in this day and age. If so, get a new scope...
Fog on the outside? Keep the scope cold, in the elements and don't breathe on it. Don't put your scope under your poncho to keep it warm and dry. As soon as that warm glass hit cold, damp air it will fog on the outside. Solution? Keep your rifle as close to air temperature as possible, use lens caps, don't breathe toward your scope prior to shooting. When it's real cold, I wear a neopren face mask. This keeps my face warm and secondarily, diverts and diffuses my breath and seems to keep my warm breath from being directed near my scope.
Even my cheap Nikon's and Bushnells have a clear view if I keep the lenses at air temp and dry...
NGH