Anytime I have a fridge roof vent to work with....I use it and mount a combiner box under one of the solar panels. I have a variety of liquid-proof strain reliefs that I keep handy for just about any size wire.
I have never had a complaint in 8 years about leaking water thru these type of connections. As most cable other than the 10AWG ship-board cable that AM Solar uses to interconnect the panels is NOT UV resistant, I wrap the line coming from the combiner box in black poly wire loom.
The other benefit on Airstreams is the availability of a wire-way just below the fridge that usually leads to other cabinets. Makes pulling the charge lines that much easier!