I had to travel over 450 miles with my two cats.  I put a disposable litter pan in the back and then had plenty of room for the cat in front.  The two openings allowed for easy load/unloading plus the ventilation screens are great for viewing them and allowing air flow.These are very  easy to clean.  The only drawback was the assemble part where you connect the tubes to each other was difficult.

Pros: Well constructed and easy  load/unloading of your pet.
Cons: The assemble part where you connect.disconnect the tubes to each other was difficult.