If you're going to boondock seriously, and before you consider solar, invest in a good amp-hour meter like the Heart Link 10. KNOW how much power you're actually using first.
You can disconnect one battery and run the positive side of the other through a multimeter with amperage capability (be careful not to exceed its rating), and by turning things on and off sort of figure out how much current each uses, but that doesn't tell you how much things that turn on and off over time, such as the refrigerator gas solenoid and the furnace fan, use on different temperature days.
Here's a good price on the Link 10
from a reputable mail-order dealer, and here's the User's Manual
you can read and get familiar with.
Even if you later decide to go the generator route, this meter will be invaluable for battery management.
Solar panels mounted horizontally flat on an RV roof provide much less than their rated output. They are also rated at very cool panel temperatures, which you won't see in the real world. For example, a 120W panel provides between 20-30AH/day, depending on time of year. That's enough to run one Fantastic Vent on medium for 8-12 hours, and that will just about offset the heat gain of parking in the sun in a smaller trailer.
IIRC, the original Airstream boondocker option was a 50A panel, about enough to keep batteries charged while in storage. They may have increased this to 100A later. I'm not sure of the Airstream options, however.
I can tell you that with two Fantastic Vents, two skylights, and the air-conditioner, there are only two stretches for panels, one about 52" and one 56", on a 34' trailer, and there is the potential for the AC to partially shade one of them.