If you're only going to be gone for four days, it would be a LOT less stressful for your snakes to leave them at home. make sure their temps are good, they have fresh water, and go on your trip. I don't see how you could keep these snakes in motion for that long and not cause them stress. even in a car, if they're in a pillowcase or some type of tub... the snakes will be able to sense the car... the vibrations and movement.

Anytime you have to "sneak something in"... you should really re-think and re-evalualte your decisions.

Sorry if my replies sound harsh, but it just seems like a lot of un-needed stress on the animal.