I'm installing two 6v battries to power the DIY weekend package I'm putting in my horse trailer. My truck is diesel and has two batteries and a 136 amp alternator. It's getting to the confusing stage of how to marry and isolate the existing circuit powered from the tow vehicle's 7 pin trailer connector and the ciruit I installed in the living quarters powered by the two 6v battries. I would like to be able to run both circuits from eighter power source and charge the 6v battries through the alternator while the vehicle is running. How can I accomplish this ? Also,do I need to install a battery isolator, a battery integrator or just a simple battery switch like a marinco two battery switch ?