There's a company in Portland, Oregon called BlaqPaks, who make one of the most innovative and practical products for CETMA cargo bikes, a rain canopy. It's a skin of waterproof fabric with huge windows sewn in and stiffeners to make a curved bubble shape. One of the best features is that the rear wall is wide open for ventilation and communication between driver and passenger. Two ingenious magnetic side snaps keep it secure, but a release tab pops it open and the whole dang thang can be rolled up and stored. Swell!
BlaqPaks also makes a bitchin' duffel bag which I recently bought and dragged all over the state of Montana. It's perfect in every way, I love it. The bag, not Montana.