For those without saddle bags, and maybe even those with them, I stumbled across this on Cabellas website and it looks like it should make a really good sissybar/luggage rack bag for longer trips or overnighters etc.   From what I can tell, it should be weather proof and for $20 it is a great deal IMO.
http://www.cabelas.com/cabelas/en/templates/links/link.jsp?id=0026022516442a&...

I was just in Cabela's a couple days ago and picked up two 18"x12"x8" (or there about) carry-on duffle type bags with two pockets each for $15.00 a piece (marked down from $40.00 per) that are going to go on the back sides of the bike. Not quite as large as I would like, but they look good and are water repellant as well as being sturdy. I just wish they had been available in either yellow like my bike or at least black. I already have one of the T-Bags with it's strap-on duffle tube sack that ties on top, for the big stuff, to sit on the back seat.

Whatever you end up with, always line them with at least heavy duty trash bags with enough room left over to twist the top shut and fold over to keep the water out. Nothing is ever really water proof.

Jack