I do wonder as a Morgan has little or no real form of sound or heat insulation within the cockpit it makes it more liable to temperature range change, so the cockpit becomes hotter and cools quicker than most cars, which may create more condensation. It certainly is more open to wind and rain whilst driving especially so with the hood up than other soft top cars, which may create different hot and cold spots within the cabin and behind the instrument panel, especially with the trads. The heaters are so directional and localised and far more effective, especially in the later trads with heated screens, I question how much warming air circulates behind the instrument panel and whether this causes the misting. I do seem remember my older trads with the front heater vents the instruments misting but only in very cold and wet weather but not to the same extent as my later newer trads. I never remember them misting just because the car had not been used in awhile as with the newer trads. But sometimes memories do play tricks on you.
I was going to write something similar if you hadn't. I don't really care about fogged instruments. But if I wanted to do something about it, it would be small hoses instead of just holes. Warm air can be fed into the instruments from behind via these small hoses, perhaps diverted from the heating air, with a small electric fan in front of the small hoses coming from a small box into which the air is blown.
