Looking great! It's almost too nice to haul around dirty motorcycles. LOL!
Having owned RVs and used their duall battery internal electrical systems, I'm secure in saying that your one small battery is not going to power much or last very long. If you're running just LED lights and the occassional water pump then, you'll be ok for a short while. I see you have the generator so maybe the 12V electrical system is not one of your top priorities.
While you're in the middle of the build is the best time to add another battery or 2. You'll be glad you did. The optima yellow tops AGM batteries are made to be deeply discharged and recharged without harming the battery. They're a bit more expensive but will last longer and perferm better. http://www.optimabatteries.com/us/en...cts/yellowtop/
Another nice thing is that you wouldn't need to vent the sealed optima batteries.
Love the updates!