I personally toss some reusable desiccant packs in all of my cases, but it's not exactly humid where I am that often.
If it's a real issue though, Ruggard and a few other companies make cabinets specifically for keeping camera gear climate controlled to keep moisture and mold issues down. They aren't cheap, but you get heat and humidity control with one. (I think the 10L size is around $200 and that'll just hold a handful of bodies or lenses.