Hey blue, If you catch a big tuna you can core it out and fill it with ice, and then wrap in a big space blanket. We have used many fish bags especially on the kingfish tournament trail, we used them a lot for toting the fish to the weigh in. But when we go out of NC for giant bluefin tuna, and 500-600 pounder won't fit those bags, so we use the space blanket idea and works. its all about reflecting the heat.
Also on a side note guys, we line our fish boxes with more insulation, and then space blanket reflective insulation. its like a emergency space blanket thats kinda thick. And we can hold ice for a few weeks. We can keep fish fresh for three days, and on the third day the ice in the bottom of the box is all frozen together with the fish. So it works!!!
Oh and these we dont fish the pro tourneys, or the BFT in my little V. For those we got a Wellcraft scarab 35. I didn't wont you thinking i was crazy. The ideas will work on the V just a smaller fish box.