No 12 Volt without converter

Gary, I recall some of your past posts and threads and from that, I can say with confidence you should not start “taking things apart.”

The chance you have a dead short in the battery cables somewhere hidden is pretty low. 
And yet to do any actual diagnosis….

Cant help you until you help yourself some. Check continuity, grounds, reverse polarity, etc. so much to do before “taking things apart.”

If it’s the circuit breaker it should by most normal RVs, be accessible. Not likely it’s buried and inaccessible. 
But again diagnose first. Continuity, charging voltage etc. 

Until you actually do a bit of basic diagnosis it’s hard to help. 
Converter feeds power to the fuse panel and batteries simultaneously. Since converter is working, the problem is between the 2 ends of the battery cables. 

At the batteries trace the positive wire until it disappears into walls. Look for a small box (circuit breaker) with the wire going into and out of. You should get the same battery voltage on both terminals of that circuit breaker If no power out of the breaker use a screwdriver blade or a short piece of wire to allow power past the breaker as a test. 

Here's a picture of a common inexpensive breaker that many RV's use. They are available at almost any auto parts store.