If cost isn't an issue, try the Aerostitch Ultralight. Packs very small.
I use the medium size of that cover (leftover from my FZ6 days) and it works very well, but is slightly tight lengthwise with the point on the back of the PCA rack I have (Vstream screen also). That being said, I can easily pull it down to cover all but the lower portion of the front tire and, in the back, pull it over the bags and pipes (I usually leave the pipes uncovered though). There's usually a lot of slack material around the back - perhaps a top box would take that up nicely. It packs up in a bag about the size of one of those 20 cd 6" "booklets"...very small. I would imagine the larger size might also work great with a top box.
Bradman, you're welcome to swing by and test it out if you're ever in the area and haven't already purchased one (noting the date on the OP).