I've ridden in two rainstorms while on the Rocket, one was a 200 mile trip on both Interstate Highways and smaller secondary highways and roads.
The Rocket is as stable as they get, I had no handling or traction problems at all. Keep in mind you should be cautious in these conditions and not push things, but the Rocket does very well. It will help if your tires still have tread to channel out water (some people run them down to almost the cord

) and they should be inflated correctly.
I think it has to do with the weight of the bike, the long wheel base, and the ability of the directional tires to channel water away from the center of the tire casing.
I passed a couple of semi's probably going about 65 mph and had no traction problems. Visability is another issue, I wish my helmet facesheild had a wiper.
I guess not every day can be sunny and 85
The bike itself was a major mess, and took hours to clean. This may be one of the hardest bikes to wash ever. I like to find the local cheerleader fundraiser carwash and let them have a stab at it. They don't do a very good job but I don't care....
PS... Sheepskin seat covers suck up gallons of water and that feels just lovely, best to stow that in the bags if you can. They do dry out just about perfect and if you shoot them with some compressed air after they are dry it blows the sand and gravel out and they fluff up just like new.