8 hour rest?

I've held 'em that long, and they were still too hot to pull. I think you'll be fine.

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?

Sounds like it's a done deal. Just be prepared for a lotta juice when you open the foil (learned this the hard way).

I rest my briskets in an insulated sleeping bag. Works fine.