+1 on the cooler thingy, had a local in Hawaii roll up to me at a red light and say "hey bradda ur saddle bag is leaking" then I told him I was using it as a cooler he just started laughing.
When I wash my bike, water gets under the lip of the lid, but never inside. But, when I go to dry my bags off, I open them, and then it drips inside, because I opened it.
I once rode in a severe downpour for 260 miles on the Ohio Turnpike year before last. I had a good 1/2" of water in both of my hard bags on my Roadglide. I've ridden in moderate rains and no problem. I guess it depends on the amount of rain and distance.