Last year I shipped 352 boxes of fish. I lost 26 fish total out of more than 1000. I dont starve them for 48 hrs. I do not feed them the night before or day of shipping. I package the fish 1/4 water 3/4 air from my pump, I leave a hose running to aleveat pressure so I fill the bags with it. I double bag the fish and use 12x5 inch bags I know this sounds long but you are then able to tie a real knot in both bags. I put 2 -3 per bag at 1 inch or so. Adult fish go into overly large bags 4-5 per bag. Overnight shipping adult and expensive fish. 90% of my shipping is Priority mail. I do not reccomend rubber bands or wire ties etc.. I have recived fish this way. The bags slowly deflate with most of the stored air releasing into the box. I also have recieved more dead fish than most some due to importing but most in bags with rubber bands or wire ties. This is my 3rd year of shipping fish and have shipped a total of 800 + boxes with less than 50 dead fish. Just my thoughts and how I do it.
When shipping I use insulation 1/2 that is used in houses as most of the lining. I have used other stuff foam etc. all seem to work well the insulation I find less messy than stryfoam.