I can remember when Carcoons first came out, many moons ago. I tried to fathom the science, but apart from filtering the air and transferring moisture from inside the envelope to outside the envelope I couldn't see the benefit. When contained in a garage the moisture will remain in the garage until the doors open, or there is a dehumidifier. So I went for just a dehumidifier. And given the faff of getting the car in and out I still think it was the right choice for me. Up to now I've never heard a bad word about these chambers, but obviously kept outside there is a ventilation/temperature difference problem.
On my Golf - kept uncovered and outside, where there is a sudden fall in temperature in the evening, the windscreen (which faces North) mists over on the inside with significant wetness. No other glass is affected. Despite various ploys, this is a feature over winter and I guess if left for long periods might cause mildew. I keep a passive dehumidifier in the Golf - blue crystals when dry, clear when wet, and this works really well.
