If you insist on having the entire flat of crawlers with you, a 5 gallon bucket with a styrofoam minnow bucket liner works great. Those large capacity(4 gallons or so?) buckets found at most bait shops. If you dont take the whole flat in the boat, the 1 gallon(approx) styro buckets also fit tight in a 5 gallon bucket.
It saves lots of spills! If they do tip over, the crawlers are usually just sitting on the inside of the bucket.
Cattin Addict.. you think those crawlers were bad, I had a 14″ northern squirm out of my hands and shot like an arrow and got underneath my flooring through the bilge area many years back. That fish was not coming out without disassembling the entire boat. The stink went away in about a week in the hottest summer months(cooked it). A few years later I did replace the flooring, and I had a perfect *northern fossil* on the aluminum of my boat! There was an entire textured skeleton. It made it all the way to the center of the boat under the flooring. It looked pretty cool