In my20' Lund I used a 30gal.plastic sryup barrel with a Rule livewell/baitwell pump 1100gph model #205F which cost about $37.00. They also make a 700gph #203F this whole set up will cost about $75.00 or so I now have a 55gal. barrel in my 26' boat.You could mount it either thru hull or make a rig off your transom which I do.
Take your barrel and cut the top out leaving about 1-1/2" lip around the inside of the barrel. This keeps any water from splashing out. Need an off &on valve, some 1-1/8" hose . Rig the pump off the transom with plywood or aluminunm{have to use your imagination here} Attach a plastic or brass scoop so that when you are moving along water will be forced into tank. For a switch I use a house light switch and plastic box.
Go to
www.rule-industries.com click on pumps and you should see live/well pumps
I used to keep 24-30 mackeral in the 30 gal. barrel with the 1100gph.
The Unorthodox Flyfisher