I saw this in a Winnebago Vectra and again in a Newmar product, but imagine where the kitchen slide goes in and out and there's sort of a trap door that opens and closes for the purpose of allowing the wires and such to go in and out and then imagine rigging that door to remain open, or even taking it off.
Both rigs I saw had cut holes in the floor such that this opening was thereby accessible to the kitties and they went down and did their thing and came back up...
I know this because at Newmar the tech happened to open the subject compartment and the cat got out of the coach.....That's ANOTHER story all together....
Maybe consider something creative like this?
How about a hole in a cabinet floor even, where you could close the door when unused?