Don't let the rain stop you. I've killed some nice deer on rainy days where I thought about staying in bed, but forced myself to go anyway. Get some good goretex rain gear, and maybe a treestand umbrella, and you can still be comfortable in a stand all day in the rain.

I ditto txmarshmonkey, I wipe my bow down and put a few drops of oil on the screws and any exposed, uncoated metal. You should be fine.