I moved a 2' arowana, a 16" Leopoldi ray, 2 yepezi rays plus others and a full reef tank with corals and inverts exactly the way described above, borrow some polystyrene boxes from your LFS and half fill with tank wter and then place your fish, seal up and go
The endlers and reef inhabitants were in their boxes for approx 12 hours
Paul_MTS on here was a top man looking after my biggies, they had a 6 hour span in the box
If you think the box with the fish will be in an area where it is cold buy some chemical handwarmers from a outdoor sports store to heat the box. Any store that sells fishing gear or hunting supplies will have them.