I have a live bait tank that pretty much fits the dimensions you suggested. It is not overly big but I can fit around 12 slimies in with no real hassels and keep them alive most of the day. Just crank up the water input. Admittedly I haven't got too serious at this time fishing outside but when the time comes I think I will be getting a bigger tank.
The kids love keeping whiting alive in it and it will soon double up a a deckwash and hand held shower.
Cheers
Mark