How about something like this. It looks to have a pass through from the cab to the box. Biggest down side is everybody will want you to help them move.
https://louisville.craigslist.org/ctd/d/lake-in-the-hills-2018-gmc-12ft-box/7716237548.html
https://louisville.craigslist.org/ctd/d/lake-in-the-hills-2018-gmc-12ft-box/7716237548.html