Just remember the rain sock that comes with these bags are not really intended for extended periods in the rain while on the road or parked. I use the one that came with my bag, as it has the reflective piping on it, but I always put the bag into a plastic trash bag first, put the rain sock on, then use a bungee net to secure it to the rack. Found out the hard way that the factory rain sock is at best, protection from a light drizzle rather than a steady rain. 10 hrs straight in steady rain had everything but the innermost core of my packing soaked.
It may work well if coated with 'CampDry' or some similar weather proofing additive... but I've still not found anything better than a cheap garbage bag, and it's under the rain sock, so who else knows right? and the garbage bags make great dirty clothes bags until you get to your destination.
8 days on the road to Texas, and aside from the bag on top of the tour pak, you'd never even know I was on a long trip... other than the Alaska license plate.