It seems that I am always taking or picking up fish...... hmmmmm
I have used all kinds of stuff.... most way to large.
My latest creation uses a CD storage box. It holds a total of 3qts of water.
I usually put in 2 qts (half Gallon) and it does very well. The box is designed with an inner lip that fits up into the lid, I am guessing this was for dust control, but it keeps splashing water in well.
I have rigged a small air stone that I run using a small pump and an a/c inverter.
This thing works wonders, I often pick fish up while on my sales route, and sometimes it is hours untill I get home. I have rear heat and a/c in my vehicle, so I try my best to keep the temp that way.
Not the normal DIY, but hey, it works fer me