I'm with the other guys in being a little suspect of the wiring.
Make sure the connector between the two batteries is the same gauge as everything else - it looks like it might be pretty thin from your pictures.
Is there no breaker panel in your trailer? Just wondering why the need for an inline fuse right off the battery.
Check that connection between the green and black wires too, if it was done poorly then that'll cause you headaches too.
The other thing to add into your setup is a battery disconnect switch:
http://www.amazon.com/Marinco-701-Ba...N04ZPCD4KWXXW9
You'll want to have that so when you park your trailer, nothing will slowly drain your batteries. (fridge lights, smoke/gas detectors) It's also a lot easier to wire one of those and simply turn the dial as opposed to taking a battery cover off and undoing a terminal.