Harvey51 wrote:
I worked hard to improve engine charging, getting rid of voltage drops in the connectors of the wire from engine to house batteries, eliminating the battery cutoff switch and its wires.
You are not going to win !
Most US vehicle designed/built after about 2000MY use the PCM to do "smart" charging of the battery. This means overall lower charging voltage.
(I worked in Engineering for one of the Detroit 3 10 years ago.)The best way to charge your house battery while you are driving, is to install a small (<1000W) sine wave inverter and run an extension cord back to the trailer and use your favorite AC charger.
You can find dc-dc converters on eBay that will take 10VDC in and step it up to >14V, but these are constant voltage/current and not appropriate for battery charging.