I fitted a Polaris setup to my Cruiser, aiming the one on board at the towbar ball to make it easy to connect to the van. Then added the other camera to the 16.49OB. Running the cables inside the drawbar, under the van, and up through the fibreglass cavity, which was a bit of a dog of a job, but ended up tidy.
Recently installed an Alpine 910R before running around Sydney. There was a bit of a bonus as the Polaris cameras integrated into the Alpine, which meant I could remove the screen from up on the dash. Also had the advantage of the 7" screen for my poor old tired eyes.
Only downside is the Alpine has to load everything before showing the reversing screen, so is not as fast as the dedicated unit, and I haven't looked at how to switch the van camera to watching behind when not in reverse.