I have kept my dob in a plastic garden storage shed for 3 years, and another Newtonian prior to that for several years. The shed is dry and well ventilated. Shower cap type covers at both ends are essential for keeping out creepy crawly beasties and the little slugs that are surprisingly mobile. Other than that it has been fine. As others have pointed out, this makes it much closer to ambient temperature out of the box.
When I bought the dob I planned to put it out there from the off. There was simply no other way a 12 inch dob (SW Go To) was ever going to be practical. Hats off to anyone who moves ones of these beasts from indoors out in to the garden for the evening. I chose to accept that it would deteriorate over time against not having one at all. Although in fact it has not yet suffered so I am ahead of where I thought I might be.
Rather against the grain, I have also kept my refractor out there as well for a the last 2 or 3 years. Now that is in a flight case (as supplied by SW - not fantastic quality but certainly good enough) so is much better protected and it hasn't suffered at all. I do definitely let it dry completely, usually indoors, if it gets damp in use before putting it away again, though.
The mount for the refractor and a previously owned EQ6, however have suffered some corrosion or rust in certain areas, especially on some of the screw threads. Even this has not been too bad and is only cosmetic. A bit of protective oil might have helped here.
So after many years of moving stuff in and out of the house, I came to realise that making it as easy as possible to get the kit ready for observing meant it would be used more and I would enjoy their use more. And that balance has proved good for me.
Of course if I had one of those lovely Taks, or some LZOS kit (drool ...) I might feel differently abut that balance.