How would you intend to fill them anyway?
Keep in mind 5 gals will only add 40lbs of weight. So would take 20 of them to get 800lbs in the boat.
$12.99 x 20 = $260. Or you can buy a 400 lbs Ronix Eight-3 bag for $127.99 each
https://www.wakemakers.com/ronix-eig...y-ctn-400.html
For the same amount of weight, and enough to make a difference, you would be way better off buying actual ballast bags.