COOLBEBE Car Seat Protector for Potty Training, 2 Pack Dry Waterproof Car Seat Liner Toilet Training for Baby Toddler, Piddle Pads Cover Pad for Strollers & Carseat (Dinosaur,2PC)

These are the ones we bought. Haven't had to actually test their effectiveness, fortunately, it's good piece of mind. Also, I feel you on the nap issue, ours is at a point of dropping his nap semi-frequently. But the car has magic powers sometimes.