Just don't, m'kay ?
Don't leave your scope outside, even if covered, for more than a night.
People think dew is just water - it isn't - anywhere near a city it is actually quite corrosive due to traces of contaminants it collects from the air. What settles on surfaces is usually an acidic witches brew of nitric, sulphuric acids and more. If you're near the coast it will contain salt and that is a disaster for mirror coatings.
At one time I had a big heavy 12" newtonian on a heavy equatorial mount (fork) whicj was big and cumbersome to set up and pack away each night. At one time over a Christmas break I left it outside for a few weeks hoping to do a lot of observing each night, with a silver padded car cover, thinking I could save myself some time. At the end the scope was in bad repair - the mirrors had to be recoated and a lot of parts were rusted or corroded.
Anything made of steel rusted. Even parts that were plated, and despite liberal application of grease and WD40. Even on modern scopes, most have nice allen head or grub screws in odd places and most are steel.
The mirror coatings were ruined, quite quickly despite having been quartz overcoated, even though the tube was parked such that the mirrors were vertical (primary) or facing down (diagonal).
If you value what you have, take it indoors. Even a garage would be better provided you can keep car exhaust fumes away from it (they're nasty too).
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