I built my electrical system around two 100Ah batteries that are charged one at a time from the alternator or from the 100w solar panel.  Switching between batteries is done with a knob that selects battery one or battery two.  The accessories can also draw from both batteries by switching the knob to one plus two which connects the batteries in parallel. 
Electrical Upgrade 
Charing the batteries from the alternator didn't allow for enough power once driving became limited.  I added one 100 watt solar panel and charge controller from Renogy.  The panel has been a great addition to the electrical setup.  

Fuse box, Renogy solar controller, and power distribution knob.

Wiring diagram detailing the van electronics. **wiring diagram does not reflect the addition of the solar panel and charge controller. If you have questions before the diagram is updated, please reach out. **

The dual batteries are placed over the drive side wheel well.  Along with breaker, smart isolator, and negative bus bar.

Renogy 100 solar panel

The main control panel houses the light switch / dimmer, battery voltage gauge, and USB / socket charging ports.  The battery voltage gauge has three positions battery 1 voltage, battery two voltage, and off.

Running the wiring for the lights, fans, and power inverter.

Installing the lights and MaxxFan.  The fan can either pull air in or push it out.

I had to drill access holes in the wood ceiling to tighten the solar panel through bolts. The stock van headliner covers the access holes.

Marking the solar panel bracket positions before drilling the holes.