As long as you keep the car at a reasonable temperature it will be fine. Snakes can be quite hardy and go a while without heat. Just dont put the heaters on full blast in say the footwells and then put the snake down there lol :2thumb:
right this is what i did for my snake transport, Jersey to Yorkshire and back again
Over night ferry (8pm till1am) snake was put in poly box, inside a pillow case surrounded with a duvet cover and a heat pack. cold nights)
journey back (heat of june) i had the opposite problem boiling hot and trying to keep them cool, put them in the floor well with the air con on in the shade.
the journey was 11 hours there and 11 hours back, the snakes did better then me thats for sure:blush:
I moved all my snakes down from Yorkshire to Portsmouth in the snow last year - just put them in rubs with a hide in and in the car, they were fine. They spent just over 48 hours in a rub since I had to send furniture inc vivs down in a van the day before I moved.
You don't want them too warm for moving anyway, they're better off kept cooler so they're not very active.
Unless you have anything that is likely to keel over on you if things aren't spot on then they'll be fine, Most snakes are not made of glass.