Either for oxygen, I use a polybox or a cardboard box lined with polystyrene, the first is the easier to do as unless you have the right sized poly you have to muck around with the cutting of it to get a firm fit.
Seal the bags super well, I band mine and then tape them down so no air can leak out. Tropicals make sure you include a heat pack, the Sth Islands getting cold at this time of the year. Label your box which way up you want it and label that its live fish. Its easier if you can deliver to the depot rather than have them pick up as the later in the day the better.
Good luck - you shouldn't have a problem.