Building a light touring set-up... any advice on a decent sissy bar/backrest bag??

[Triple]

This is my current set-up:



with my National Cycle F-16 "touring" windscreen (which is fine for brief jaunts on the highway):



plus this (still need to mount):


and this (still need to mount):



I think the soft bags will be adequate for 1-5 day runs, but I need a bit more space. I am thinking a good quality, waterproof sissy bar bag would work. Any suggestions? **BTW, I plan to take 1 week in Deals Gap, the first week of August.*** Of course, I'm riding down.