I use a hack I saw on instagram which involves strapping in the potty in a similar way as you do with his car seat in a spare seat at the back. We use when we’re out and about in the car. You can put a nappy on the potty to catch the waste too for easier disposal. Handy for days out in the car or trips to the park. Ps you would use this in a stationary car x
Make sure he goes before you get in the car and put something on the car seat in case of accident.