How about a backpacker's tarp? It scrunches down to almost nothing and you've got a piece of gear you can use for other things. If you get one big enough you can have an open air shelter for both you and your bike.
the tarp is interesting idea. I also like the Nelson Rigg stuff, just curious what others are doing. My main goal is to keep rain and dew off the new corbin I just got. Bike is garage kept other than when I am camping.