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Metal roofs need sarking/insulation to prevent condensation forming on the underside of the sheets. Metal is often colder than ambient. Add to that humid air and the temp dropping below the dew point and you get condensation.
Put some sarking/insulation under the dome sheets to reduce it at source.
You do get condensation on your gear on really humid nights when the air temp goes below the dew point. That will vary according to location but where I am it happens about one night in 20. That is with the roof open.
I lose part of night to dew on the mirror about one night in 30 and only for a small part of the time.
My observatory is on a slab, I run a fan at the base of my scope to reduce local seeing effects (not sure it does anything), I have air cell insulbreak insulation behind all walls and roof.
Greg.
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