We bought one of these, what I call a cat condo:
https://outofsightlitterbox.com/
W have an ERA 170A and I pulled out the sofa and installed the condo. Our cat took to it pretty quickly. His litter went into top and you can just open the lid to clean it. Good storage in the bottom. I velcroed a small rug to the lid and he often hangs out up there while traveling or he lays inside the entrance on the mat (to stay out of the way of our two labs). He shares their water and we keep his food on the rug on the lid so the dogs don't get to it. Ours likes to be outside but we keep him in when traveling.
Depending on the model you choose, I would imagine you could pull the bench seat and replace it with one of these (assuming the seat isn't hiding a water tank or something else useful).
Here is a shot looking inside the sliding door.