If you think it's going to be very humid and there is a risk for your gear, then you could try to wrap your camera and lens in a plastic "bag".
If you have a bit of time before the event and think this might help, you could try and customize a large zip-lock bag in order to contain your camera and lens while leaving the front element and maybe the viewfinder uncovered. I found this link with a detailed how-to and some pictures. You could try it out!
EDIT: Certainly it's not water-proof but I think it can help quite a bit. This might be a bad idea though if your lens is not Internal Focusing and a downside is that you might have a slightly harder time rotating the lens barrel. Also you have to be careful to allow enough room for the lens to fully extend. But all-in-all, it's a cheap and easy way to protect your camera against sand, dust, humidity and maybe even from a small drizzle.
I'll actually try it myself as I know it will come in handy at some point. Hope this helps!