I have a bait bag on my transom which we primarily use for drop back mackerel; but during tuna season before the marlin show up I'll use it when I have 4 or more anglers. It will hold 1/2-1 scoops comfortably combined with the 1 1/2-2 scoops my standard Blackman tank holds and I'm set. With 2 of these, one on each side, you would have plenty of capacity. There's a Blackman on my dock that has the 2 bags without the Main Deck Tank and he seems happy with it.



I had a hard 20 gallon fiberglass tank I set on my swimstep and tied it down however in a large following sea one time coming home it came unbuttoned and I never saw it again.