I live in western Washington, not exactly dry. I have an alum tool box, but I keep contents in plastic boxes. Insures they stay dry, but also serves to keep things sorted/categorized. If I need my small tool set, I just grab that box. If I need my ratchet straps, I just grab that box. You get the idea. It's a system that works well for me. As to your question, I've never noticed water inside the main box itself.