and those little heat packs you can buy at the hunting store works good..Thats what the hatchery puts in the box when we get them in the mail....Just make sure the sock is secure so it won't roll on them and kill em...
I would put like a old tee shirt or somthing in the box...so it's not a bare box...they should be ok just keep them out of any cold drafts and such....Keep the car warm..