Thank You for the reply. I have had sail boats before that have meters to show voltage of batteries and most cars have volt meters to verify the alternator is working and I thought it would be nice to do the same for the auxillary batteries but you are right, it would be easy to use a multimeter to verify the generator is working. I also thought a voltmeter would show the level of the batteries and if they needed charging so they wouldn't be damaged.
You answered another question I had because I'm new at owning a RV. The alternator charges the auxillary batteries as well as the engine battery.