Actually, I might extend the coverage to the top of the bucket. I used some reflectix to make a chute under my mill to keep the dust down a bit - it helps. If the exit from the mill isn't bound in some way - the dust really gets out of control. I also made a skirt out of a malt bag, but took it off - it helped keep the dust out, but really got in the way of pulling out the bucket. Some thin plywood will add some stiffness to your design and help to control the dust.
Now if you are out of stainless screws at this point... you might need a few more.