Qld, beautiful one day, swampy the next. It is a concern that's for sure. fortunately my downstairs is cooler and drier than the rest of the house. I tend to have a small pedestal fan running most of the time I'm down there so that helps a bit. I like the idea of the silica gel packs under the dust caps.
Robert, re your plastic sheets covering the scopes. You don't find that they trap moist air under them???? I use old sheets as dust covers. Plus I reason they are absorbant to a certain degree and "may" help prevent excess moisture getting to the scope
Don't know for sure though.