A quick tip I learned 4 years ago...
I use a heavy rubber lens cover, zip tied to my scope, along with flip top scope covers. Even the best scopes in snowy conditions get moisture between the caps and the lens. Ice will form. Internally the scope is still clear. I put a small piece of clean/dry toilet paper in between the hard cover and the lens, then the heavy rubber cover over the scope. Since then, when I have to look through my scope, my lenses are clear. I think the TP absorbs moisture and is needed, it's also available to quickly use on the lens.
Going from hot to cold, in the horse scabbard and out into 10 degree weather reeks havoc on scope lenses. The other necessity is some stuff called scope dope. Waterproofs, fogproofs and cleans your lenses.