One gallon per fish you catch for a limit. 48 quarts is only 12 lbs of fish. Especially if you catch the fish the first hour your fishing and they sit in there for the rest of the time. But that would be the day you catch 3 4 pound fish and think are they going to stay alive? Don't want to think about it personally.
You just have to do your best when you have those days that go your way and you have some quality fish in the livewell. We have a decent size cooler and the spray bar setup, like most on here do. As long as you keep the filter clean, add some fresh water every hour and some "Catch & Release" blue type stuff, you'll be fine. Add a few frozen bottled water in the Summertime to keep the water cool too! It may be a bit crowded (if you're lucky), but you'll have nice lively fish at weigh in. We've had 15 lbs in ours and have not lost a fish in 3 years following the above guidelines.
Good luck and PM me if you have any questions about what we use specifically!