If the car's a-rockin', don't come a-knockin'. And even if the car is sitting completely still, please do not disturb because it probably means I am sleeping like a cherubic child of Zeus on my Fuloon inflatable back seat mattress. The inflatable air mattress doubles the size of cars' rear benches, and also makes them more comfortably contoured for butts lying horizontally rather than butts seated upright.
A bottom leg with center cutout provides stability for the side of the mattress not supported by the back seat itself so no one makes one false roll and wakes up with a mouthful of autumn leaves from a floor mat. Flipped, the Fuloon bed also doubles as lawn seating and a raft when you're not using it to sleep on the cheap during road trips, or normal life until your mama says fine you can move back in as long as you promise not to swap out the brownies she made with the brownies you made before her garden club meeting again. Oh come on, Mama! I thought those ladies were supposed to be down with plants and the dried herbs they produce.
The back seat air mattress fits most car models, and measures 53" long x 34.6" wide x 16.5" high. It comes with a pump for inflation.