for my 6hour drive back to uni i used a large plastic box approx 50litre but with about 25litres of water in and i had an air pump in it an spare water in bottles just incase i wanted to change the water half way and to help with the transition from very hard water to very soft water. I also put a clean bin liner around it to block the light and a peice of bogwood that wedged in tightly (tight is important because it will move around otherwise) i then wrapped some towls around it.
It held temp brilliantly, drop by 2 degrees Celcius and all of the fish survived. it had 12 embers 5 precilla tetras and 15 corys a bamboo shrimp and a clown plec. I kepy my albino red tailed shark in a large back that was in a 'cool' bag