How to wire up batteries, isolators, Ah requirements, etc, is not really RV specific, so tough to tell if your tech is confused or not.
You should have 2 start batteries under the hood, direct wired in parallel to each other. 'Cause it's a diesel.
House battery(s) presumably are in the coach. They should have a + wire coming from the start battery (or from alternator charging lead or fuse/junction block, however it is configured on your machine), likely with an isolator to keep the house batteries from draining the start batteries.
Additionally, house batteries should also be hooked to your converter and DC fuse panel for the house loads/charging.
Hope this helps.
