[flybouy]

Check the battery disconnect. When plugged into shore power the converter supplies 12 V.D.C. and you said everything works when plugged in so the converter is O.K. Sounds like you have the power from the battery interrupted somewhere so get a VOM or test light and start tracing it out. On another note, you stated the battery has plenty of cold cranking amps. That is useless in a trailer as you aren't starting an engine. What you need is a deep cycle battery and the more reserve capacity the better.