Review on Enchanted Home Pet Orthopedic Sturdy Backseat Extender with Storage: Black, Large (51 - 100 lbs) - Ultimate Comfort and Convenience by Kara Hans

This extension is used in my front seat where my shep likes to sit with his shotgun while driving. She's strapped in but her now big ol' ass is too big to sit comfortably so this extension is a great idea. The only downside is that it's too wide. It fits very well between console and door. Cannot be opened if the door is not ajar. Otherwise, it will support the 80-pound GSD's front legs and upper chest while her head is out the window and she enjoys the ride. I haven't tried it on the back seat yet, but the distance across the width is the same. I suspect that in terms of coziness, I'll have the same problem as in the front seat.