@bhermes,
your 12 v system cant deliver much ampreage anyway so, whenever you are travelling , and you run out of gas, your computer would sense that and turn the system to 12v (This only works while theres a charge going into the 12v system).
I believe that your gas system should operate the frig and the and water heater. However, unless you dont have some power from somewhere, you wont have lights at all., since on ours, all the lights are 12v. SO youd best take some 120v lampos to plug in.
You will ahev hookeups?