The boat bag of all boat bags
"This is what all the other boat bags want to be when they grow up. I have used several from different brands, and previous versions of this bag for the last 15 years. If it is raining you will need to zip it closed; water will collect just inside the bottom half of the zipper, and then wick backwards towards the inside of the lid and work it's way up into your stuff. That said it does a good job keeping splashes and very light rain out without needing to keep it zipped shut all the time. The hard bottom holds up really well sliding around on the floor."