Yes the key is to let the dogs see one another at all times, as in maintain visual contact, otherwise they panic and carry on with the whining and other assorted antics. Just being able to hear one another simply doesn't cut it.
But installing a glass door farnorth?

yeow! Best you don't ever decide to tot up your expenses on those hounds, lest you feel faint! Perhaps that should be sent out as a general caution to this crowd as I suspect we all spend more on the little darlings than we should!
Good luck with the season and getting a decent night's rest. Only 2.5 weeks more to go.