JJM5017 wrote:
Essentially I have good 12 volt power when the ac/dc converter is plugged in directly but otherwise have no power in the trailer (from battery or from 110v).
This small part of the problem sounds like the inline circuit breaker on the bat+ line (hot lead) is no longer functioning. With the battery installed, you definitely should have 12V functions, lights, water pump, etc. The circuit breaker is in the b+ lead and usually attached to side of the battery compartment. Just follow the B+ wire until you find this breaker.
Let know if you need a picture of what you should be looking for.