I have special fish carriers which I believe were originally made for bait buckets.
They are 6 gallon buckets lined inside with styrofoam inserts.
For long distance trips, I drilled two small holes in the lids, and placed a airline with an airstone down one of the holes. I then duct taped a battery-powered air pump to the side of the bucket and connected the airline to it. The other hole permits the release of air so the lid does not pop off.
I always kept at least one in my work van at all times.
Now, this is a story which will get me branded a liar, but it happened:
One day I noticed the carrier was heavy - too heavy to be empty. It did not have an air pump attached, so I couldn't figure out why it weighed so much.
I took off the lid and, to my surprise, there was a pair of gold severums in the carrier, in about two gallons of water.
I checked my schedule for the previous week, and found the severums had been in the carrier for ten days! I took them out of an account and forgot they were in the van.
This was in the summer. I was a particularly hot summer, with temps getting to the 90s on several days. And my van is a dark blue, so it gets really hot.
The severums were fine. I placed them in another account and they lived for years.
True story.