what kind of propane fridge was in all those campers that didn't work? there is nothing really high tech about them...you provide heat in the right place, make sure the other places have ventilation (a computer fan helps), and presto, cold beer.
I would think out of all of those campers you listed, at least one manufacturer would have known how to correctly install a propane refrigerator.
I just tested our new Norcold 641 3 way propane fridge that we will be installing in our flatbed camper, and it cooled down to -10 degrees in about 4 hours, with ambient of 80 degrees.