You are going on a big trip on your motorcycle, but you don't want to spend a lot of money on waterproof luggage and are wondering how to keep your clothes dry? ... so, here is how I did it.
Start with a 5'x5' canvas drop cloth from Home Depot. It has a leak-proof backing, which will be the inside of the roll.
Get some waterproofing spray and spray on the non-backing side, the canvas. This is for extra insurance against water.
As a bonus - no scratches or rub marks on the chrome!
Everything you need to make it (except the bungee cords):