carry a rag impregnated (soaked) with silicone spray, and wipe down your blade after every use. I use my (1095 carbon) blades all the time near the ocean and have never had rust. Any spray that woodworkers use on tablesaw blades is gangbusters!
Yep - I always hear about how badly carbon V rusts, but I've carried several knives made from it while backpacking along rivers in that thick Georgia humidity where you're more swimming than hiking.
Keep the blade oiled up and you'll be fine. Actually, that's one thing that makes me lean towards leather sheaths a lot - oil your knife regularly enough and the inside of the sheath gets pretty well soaked with oil, and simply putting the knife in the sheath gets some oil on it to help prevent that rust.
