We bought a good waterproof mattress protector when I was pregnant with my first. My waters have never broken until I got to the pushing stage (at hospital) so it was never a problem, but with the amount of milk leaking and baby perk afterwards, the protector is a good investment. I have never worried about the car before, but as we are buying a brand new car for this baby, I will be putting a towel on the seat JIC. Statistically The chances of your waters breaking before established labour is really low, so I wouldn't stress too much.