Keep the ice box for now, re-evaluate later. Use your existing portable to freeze more ice as needed? That's what I do when my 3-way refuses to do its job in hot weather. Small portable 12V unit sits between the cab seats, runs when I drive, freezes small reusable Blue Ice units.
If you do decide to swap out your icebox, measure to be sure that both it and the proposed replacement will fit through the camper door. Someone on this forum posted a video on this a couple of years ago. It was not the simple plug-and-play that "pre-wired" implies.