While I try to use IBCs exclusively since I get them very cheap and they work great, My recommendation would be to build a large tank from wood and pond liner for your fish and then use the cut off IBCs for GBs. Another suggestion if you have the room is cut an IBC in half and connect the halves together via a SLO pipe and keep fish in both sides. You could separate them by size then if you want. I can send you a diagram of how to hook that up if you like.