My snake has become quite the little traveler lately.
I have a 15qt tub with air holes drilled in that I use. I put a cloth on the bottom and one of her hides in with her. I then preheat the car and dress like it's the middle of summer. When walking to and from the car, I wrap the tub in a blanket. Exposure to the cold air can cause an RI, though that is what you are going to have checked out, but it certainly can't help. I usually leave the blanket loosely fluffed around the the tub so it feels more like a burrow.