I haven't had the pleasure of visiting Florida yet but if it gets as humid as it gets here in the Philippines during the rainy season, then the following tips might be helpful.
First, for paintings in progress:
During the rainy season here, it gets very hard to dry a painting because the air can get very saturated with moisture. Even dry paper when exposed to the air becomes moist (even inside the house with closed windows). This trick is for "seemingly" dried painting in progress. Normally, during dry season, I just use tracing paper to cover the painting and keep the dust off the painting surface when I'm not working on it . But during the wet season, sometimes when even the tracing paper gets moist, I would take to using a plastic sheet instead. While plastic may seem waterproof, it is actually still permeable to some moisture... just that it keeps 99 point something percent of it off. Problem is, when the plastic is in contact with the painting, some moisture can get in and this can get trapped and create the perfect atmosphere for mildew growth. The thing to do then is to use spacers to elevate your plastic and keep it from touching the paper of your painting and also this creates a pocket of dry air above your painting. You can use clean bond paper or better yet, scrap watercolor paper to make a cylinder that can stand harmlessly over your painting to act as elevators. I've cut out the painting already by the time I took this picture but you'll get the idea.
So when you place the plastic protector above, it should look like this... tented. This just demonstrates the use of one spacer. But I sometimes would put four or six of them on the painting - specially for bigger paintings - to make sure none of the plastic is in contact with the watercolor paper I am working on.
I haven't had any problem with mildew since employing this method. Also I've taken to using distilled water in my spritzer instead of tap water. Tap water may contain contaminants in it that later breed mildew so I try to minimize all the risks. No prob of using tap water for the wash water, just make sure your water holder gets regular cleaning too so it doesn't get a slimy film on it... microbio stuff.