I have these Nelson Riggs bags from Tonker and have been pleased.
http://www.tonker.com/shopsite_sc/st...ddle_bags.html
Large, maintains shape, waterproof stash bags, lots of internal pockets, nets, affordable, fits the Bonneville. I've taken a couple 3 day trips with them and they've performed.
The only thing that might be a problem is if you carry a passenger. Straps go across the seat between the bags and might be uncomfortable to sit on.