I used to backpack up to Amacalola Falls up in your area back in my misspent youth. Didn't have the money to have a boat on Lanier.
Anyway. These electrical problems are hard to diagnose over the internet. I would recommend a good RV tech over an electrician since many electricians don't know a thing about RVs (though some do).
There are some things to check. You want to be sure that the neutral (white) wire for the circuit is properly connected to the neutral bus bar. If loose, corroded, or disconnected, that's probably your problem, or a good share of it at least. The other thing to check is that the breaker box in most Airstreams -- whether it's the factory box or one added later -- requires a jumper between the two hot "line" connections. If that's missing or loose then half the breakers won't work. In a stick house, or trailer or RV wired for 240V 50A service, the two hot connections are opposite sides of the neutral, but in your setup you want them connected together since your shore power connection is 120v.
Post back here and let us know if that clears it up.
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