Or a heavyweight polybag, such as the ones you get your trannies back in from pro labs (well, Multiprint anyway). Cut a hole the size of the lens (most of mine are 77mm fronts) and a slit down one side to get your hand in. A rubber band round the front - job done. I keep two in my rucksack for when I am afloat taking boat to boat pics and I need to keep the saltwater off the camera. Works a treat - FREE!
Just a thought - the kind of black bag photographic paper comes in would work too - and smels nice!