I knew someone would eventually ask that! :B
We keep a small Tupperware tub with a lid in the truck. It doesn't get used often, but I'm always glad we have it when it's needed.

In the camper, I donated one of the storage spaces under the dinette to the litter box. I cut a hole in the seat to give the cats access to the space, and I use the outside door when it's time to handle the litter box chores. It beats having it on the camper floor or in the shower.

I haven't heard a complaint from either cat about the headroom under the dinette seat. :w
:):)