Hi btallon.
Sounds like your batteries are kaput.
As John said have them load tested, and then most likely replace.
As for the drain.... Not easy to find. There are a few "phantom" loads in a new trailer but unusual for them to drain a set of batteries overnight. So that makes me believe your batteries were bad from the git-go. Maybe dealer had left them drained too many times, whatever.
After getting new batteries you might want to consider a dis-connect. This is the one I use but there are many types and all do the same thing.
https://smile.amazon.com/Ampper-Batt...%2C1145&sr=8-5
That way there is no drain on the batteries when not in use.
Good luck. Hope that helped.