The most effective approach is the full ScopeShield neoprene cover, which keeps the ambient air, moisture and debris away from all of the scope surfaces.
Unless the ScopeShield forms a gas tight seal between lens and air, damp air will penetrate and fog the scope or get liquid water on it at times of high humidity cold. Saturated air close to freezing temp is tough. A good test would be to walk around in brush for an hour in 100% humidity 33 degree rain with a ScopeShield on the rifle, then hop in a vehicle for a one mile drive, then get out in the rain and hunt some more.
If the ScopeShield does form a gas tight seal over the scope lenses, it only protects the scope until the cover comes off. Then saturated air has access to the glass and will be locked in next to the lens when the cover goes back on.
What about fitting a Michael's style rubber sealing disc inside the ends of the ScopeShield?
Fir needles "comb" water out of saturated air, forming drops large enough to drip from each needle every minute or so. Liquid water forms on virtually every surface, every hair and fiber, yet it is not raining. That's a different problem.
I'm glad you are working on a solution. Our extremely wet conditions represent a small minority of hunters and small a market. Some solutions adequate for a majority don't work as well in specialized needs, as is normal for most of life.
