I use a SportPet pop up soft side crate. Buy the 'large' size.
Folds flat into a 12" round when not in use. Found at walmart.
https://www.walmart.com/ip/SportPet-Pop-Open-Kennel-Large/5192526This makes a great cat crate they love being able to see out all around them. It was the ONLY crate my Siamese agreed to stay in in the RV!
I put the litter box at the back and food/water/bed up front. This keeps any stray litter pieces IN the crate. If you look close I also buy the cat litter box with the open high side cover. Works great on keeping the litter IN the box.
This also doubles for securing cats too. Mine rides in it when we are traveling in the RV for their safety and mine. And if you have people going in and out the RV for a BBQ etc I also secure the cat in the crate so he doesn't get out and lost.
I made a shelf along side the bed to place it on so it did not take up any of my coach space. They are real happy and content looking out the window.