I used to do Solar installs on Airstreams and always came down the refer vent stack. It is the best way to get inside the unit without penetrating the skin. I would drill a quarter inch hole, in the fridge vent flange, the part that sticks up thru the roof. Insert a rubber grommet and feed the wire thru. Do this on the roof side so it cannot be seen from the ground. The biggest drawback about pulling the new in by pulling the old out is you will be disturbing a seal that was created many years ago and does not currently leak, as well as the possibility that the old wire may snap or snag in the roof while pulling and cause a void in the insulation.
Just my 2 cents worth, but I would just run it down the vent. It will not adversely affect the refer and is much eaiser than other methods.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato