So just before the winter rains I filled ten 6' long sand snakes with Quikrete gravel (harder than sand to leak out when they get old) and they are great. Nice even distribution of weight in the bed and smoothes the ride out too. But for flooding rains I need even more weight and have some extra bags that bring the total weight in the bed to 600lbs. Problem is, the bags aren't gonna hold up much longer. I don't want more snakes and much of the time these will be stored in my tool shed however, I do wanna place em in something that won't eventually rot and fail after sitting in the elements for a while. I also want to keep the general shape of the 50lb bags as they are good for securing cargo. I loooked at various plastic bags and ruled them out. I don't wanna spent coin on dry bags but there must be something in between that will last...............................right? Any suggestions? Gotta be tough so they can be tossed around in the bed.