When I had to get some hatchlings from Darlington to the south coast, I put each in a cricket tub with some crumpled paper towel, put the tubs inside a small Critter Carrier type tub and packed them round with an old towel to stop them moving. I then put the Critter Carrier inside a cool bag - no cooler inside, I hasten to add, just an insulated bag to protect against extremes of temperature. I happily carried this setup onto a train and got it home without comment from other folks and without harm to the Corns.
If using this technique for an adult Corn, I'd put it in an old pillowcase straight into the Critter Keeper and pad it out with towels. Put the insulated bag on the passenger seat and secure it in place with the seatbelt. Make sure you don't use the heating or aircon during the journey and the Corn should be fine. Also, if you park up to take a break, make sure you park in the shade to avoid the temp building up inside the car.
