My wife and I figured out something similar when we drove 1638 down to Rally 8, only we used messenger bags. Mine was from Aerostich. REI also makes a number of soft nylon bags that would work. The GT saddle bag is nice, but too small. I think to be really useful, the saddlebags should be 5 x 14-16 x 24-26 inches. That really fills the space between the seat most efficiently. At that size, it's amazing how much stuff you can carry - in conjunction with the car cover bag in the "trunk", we had no problem packing a week's worth of clothing (including some "dress up" clothes) and everything else we needed.