I highly recommend bagging your snakes (cloth "snake bags" or pillowcases), then keeping them in foam cooler boxes (or "ice chests") with some padding (like a towel or crumpled paper) under the bagged snakes. Don't crowd them, & never put small snakes in bags in the same box as larger ones, as the larger ones can end up on top of the smaller ones, causing their demise.
If using a foam box, put a small air hole in it- if using an ice chest, put a bit of tape in the top opening so the top doesn't shut quite tight. I moved with 16 snakes halfway across the country some years back this way, & the snakes were relaxed & safe. When I stopped for the nights, I'd offer them a drink of water, but all stayed calm & mostly slept.
It's essential to protect snakes from excess heat & cold- sun streaming in thru car windows can kill a snake, or cause permanent neurological damage. They NEED the insulation of a "cooler"- even for a "short ride in the car" because you never know when you might get a flat tire, or have other travel set-backs. They're easy travelers with just a bit of planning.