Something still sounds wrong about your battery wiring. What happens if you disconnect one of the two batteries? Do the systems come alive with only one battery hooked up?
As far as checking the voltage at the coach you would check on the battery posts that have the wire labeled as "to RV" in the picture below. 12v batteries in the left picture, 6 volt batteries in the right picture.
You said you have 6 positive cables to two different 12 volt batteries. That is fine as long as the two batteries are linked together positive to positive and negative to negative.

You said your chassis battery reads 0. That battery will have to be replaced.