I'm actually thinking about just mounting a plastic tool box, or some kind of hard case trunk. I figure some tool boxes are waterproof or darn close to it, and I can get one for $12 or so. Anyone have good mounting system for tool boxes? If nothing else I'll just use it as a waterproof place to stash a bag that I pull out and go with, but it'd be nice to be able to put it on and off quickly.

I'm sure there are purpose-built bike hard trunks, and I'd like to see those too, but I'm assuming that the price goes from $12 to $120 when you put $3 worth of custom clips on and say "bicycle" in the name.