We have found that by far the best cover for keeping your scope lenses clear of moisture and debris is a neoprene scope cover.  We are able to source the Hammer Scope Cover from a made in the USA veteran owned company.  The Hammer Scope Cover will fit scopes from 12″-14″ long and up to 56mm objective.  It comes with a buckled loop that keeps you from losing your scope cover in the heat of the moment.