This is what I have been doing.

I use Styrofoam boxes and it works great. There are some heavy duty ones for $20? that I like. You spend lots of $ going there so get the nicest box for a few dollars more.

Where to find good selections in Soldotna:
Fred-Myers, Safeway and there is a good fishing/Hardware store near Safeway (Can't see it from the main street).

Excellent vac-pac, deep freeze and smoke place: www.tustumenasmokehouse.com
Tustumena smokehouse 6 miles south of Soldotna. Going S. the main office is right on the highway after tote road or take a right on tote road to go to the processing center. You can also vac-pac it and take it there for freezing.

Another good vac-pac, freeze: www.deepcreekcustompacking.com
Deep creek custom packing
Mile 137 Sterling Hwy. In Ninilchik. If you go for halibut you will be in that territory.

Last day take it out of the freezer and pack it in and use LOTS of duct tape. Take it to the airport and put it in airport freezer if you have a long delay.

I have brought in fish for many years with no problems. I use the Tustumena smoke house and the fish is deep frozen. He recommended no dry ice. Last time I got back I had to wait over 1/2 day to get my new freezer and the fish were still as hard as rock.