I would use a good sealing cooler, something that will keep the air in. Heatpacks aren't a bad idea, I'm not sure if you can find actual heat packs local usually you have to order them online. You might be able to get hand warmers.

They sell handwarmer packs at Menard's here. I'll get a few to have on hand. Thanks!

Kyle

Don't forget to bring a lot of cash!   In all honesty, your corals will be fine in the cooler.  A heat pack is nice but not necessary.  Even at this time of year, I still ship corals overnight w/o a heatpack.  Corals do better in cool weather vs. warm.

Thanks for the tips. :-)