I use a 55 gallon plastic barrel cut down to about 2/3's its size with a recirculating bilge pump setup. Last year I was able to keep about 30 alive for hours. I bought a Keep Alive aerator from Mike at Cape Cod Tackle this year. It will be better and easier with that system. Mike sells complete setups at a reasonable price too.
http://www.capecodtackle.com/