i have found over the years that putting the scope under your arm or placing clothing over it to keep the rain off will cause fogging.even letting the gun and scope get warm in the truck on the way to the hunt then taking it outside into cold or freezing temps will most certainly cause a scope to fog inside.i leave my rifle in my truck overnight to insure it will be the same temp as outside.if i have to use the defroster to clear the windshield,i turn the thermostat down to just enough heat to keep it clear.scope covers will only keep rain off the lens.