Run your frig off the propane, it is cheap, and will save your battery. On our 2004 conversion van, we had a 450W inverter, and it ran the TV and charged our phones, laptop, etc. We would watch 4-5 hrs a night of TV, use the lights sparingly, and water pump occasional. It would drain the battery to fair or good. Next day we would drive to our next destination and charge the battery up, while also running the frig on battery. Depending on your use and what you want it for, a single battery can work. Doing it all over again, we would have bought an AGM battery with more amps, maybe even 2. We also have a gen and wouldn't be without one. Comes in handy when we stopped somewhere and needed to run the AC. We also used it on occasion to charge the battery.
We recently upgraded our 2004 for a 2013 with 2 AGM batteries, solar panels and generator (won't be without one). The frig is an electric only and the TV is 12V. With our current setup, we don't have to worry about draining the 2 AGM's. Also, wouldn't be without a bathroom:)