I thought these might prove useful to the next person with this dilema down the line. Bit more heavy duty than alot of the stuff sack style bags out there. I personally use a Kelty Daypack strapped one my rack.
http://www.maxpedition.com/store/pc/...06.htm#details
http://www.maxpedition.com/store/pc/...ack-26p474.htm