Lol, how do you do it? As far as kitty litter? Do you have a box in your truck or walk them like a dog? My cat, KitKat, aka Maumau, is afraid of the outside world so I had to keep a litter box in the truck. I tried a harness on him a few times and all he does is plop to the floor and freezes.
Litter box is in front of the passengers seat with Fresh Step clumping litter. Gets emptied 2 or 3 times a day. I keep a 10 pound jug on the truck. They stay in the truck. And go into full on frenzy at times. I'd be very leery about letting them out anywhere, cause something could leap out of the bushes and it would be all over.
Yep, that's how I used to do it, except with arm & hammer brand. I had to slam my brakes one day. He was sleeping and flew off the seat and slammed into the corner of the box of litter. He's had a lump on his ribs since. That's when I decided to keep him at home. I felt horrible