traveling computer in hot car

How do I keep it safe in the heat of the car as we drive?

If you're ok being in the heat of your car as you drive then your laptop should be more than fine.

Now, assuming that you leave your MacBook in a hot car while parked, short term, you aren't going to do much in the way of damage. If it's on, it will turn itself off if the thermal limit is reached. If you try to use it while hot, keep in mind you will be bringing it near to to it's thermal limit very quickly.

Prolonged exposure is another thing altogether. Keeping your MacBook stored in a hot environment won't really damage the components (logic board, keyboard, etc.) but it will shorten the life of the battery.