Davedd gives some good advise I started the about the Roadtrek Refrigerator it is 110v or 12v. It will run totally on 12V's. The Roadtrek is not you normal RV that Cost 350K Class A. I would not have the batteries installed under the Bed Very bad ideal. As a Firefighter most fires in RV Come from the Hot Water Heater (GAS) or Refrigerator (GAS) when people don't check or do maintains on get GAS chamber clean out. The Roadtrek Don't use this type of system.
Remember the Roadtrek is a Truck the M/B warranty is excellent with lots of history and road miles problem free. Normal wear and tear is not cover on any extended warranty (brakes tires batteries etc) RoadTrek warranty the unit against water leaks and electrical wiring they put in, the solor convertor and batteries inverter is cover by the Manufacture this is normal in the RV World.
The dealer you buy from will do the first year check. If they are tell you that putting 4 batteries under the bed is ok I would not buy from them I would run away.
Call Roadtrek they are very good on answering question in one day or check Roadtreking.com The two extra batteries they install are located under the back in a tool box with ventilation. Batteries normal last about 5 years I would not want a 6 battery bill. Batteries are not maintain free a good check is 80% at 12V starting at 13.5v I have see batteries get very HOT and exploded if incorrect chargers or low water. Do some Reading on what 4 Batteries will do
normal 3 to 4 Days. The biggest power is Coffee pot, A/C or Micowave. I have live in a 30 AMP Class C Full time Starting 2007. If you start the engine it will charge the battery in 1 to 2 hours. Hope this Helps Safe Travels