I have a similar product with the hard bottom that extends the area my dog has to move around in the back seat area. I agree with your assessment, it makes traveling with your dog infinitely better for you and your dog. I take my dog to either the dog park or for lake walks nearly every day so my dog cot is pretty much in place 100% of the time in my Cherokee.
The real reason for the mesh part is the airflow through. As you can see in this car, there's a vent for the rear which would be blocked without the mesh
An unmissable item is a seatbelt leash. You just click it in the seatbelt housing and attach it to your dog's collar. It gives him plenty of room to stand, sit and lay around without him being able to jump anywhere. Also in case of a car crash, he won't become a projectile
It may work without attaching it to the rear headrests. You could probably just fold the back protection underneath the base. The straps only hold up the seat back protector, the base is sturdy enough where it would stay in place. They may make something more suitable for your situation
