How long did the cook take?
Wrap it in foil or plastic/foil. Put it in the smallest cooler that it'll fit in...like a drink cooler. Then stuff said cooler full with towels. Close the lid & leave it...don't look...you want to keep the heat inside.
If you don't have a small cooler, but you do have a large cooler...after foiling, wrap the whole thing in a large towel. Then wrap that in a larger towel. Then into the cooler & fill as much of it with other towels as you can.
For an 8 hour rest you can't insulate enough...pack as many towels around that things as you can.
So again, how long did the cook take?