Poty Stops with Cats

We started bringing our cat along on camping trips 4 years ago. She's not a great traveler - no screaming, thank goodness, but she does tell us all day long that she'd really rather we were all at home. :) She is fine in the trailer when we get settled for the night, and when we have longer stays she is ok - though probably bored (smaller TT than we used to have) when we go out sightseeing & leave her in the trailer by herself. We don't have a litter box, water or food in the truck while traveling, and she stays in a soft-sided carrier with large screened areas, the size for a small dog, so she can sit up in it, turn around without difficulty, etc. We carry her between truck & camper in the carrier; she does wear a harness & leash when we're underway, but has never been trained to be outside with them - and doesn't like it much. We usually have lunch in the trailer in a rest area on travel days, and we bring her in with us & allow her to roam. I'll put down a little water for her, but she usually doesn't eat or drink or even use the litter box until after we're set up in camp late in the day. She seems fine that way.