When the battery hits 14.2-14.4 volts continue one more hour. Amps will be tapering off and it gets to be a trickle charge soon enough. This is probably a 2 to 4 hour charging period. Often people run the generator when preparing a meal so the microwave and other appliances can be run at the same time. Watch the quiet hours as you don't want to start a 2+ hour charge 20 minutes before shut off. You will find a rhythm that works for you soon enough.
Costco GC2 work great for me. RV should come with at lease 2 house batteries with a residential fridge. I would ride them hard and use them up before you spend money.
I would tend to just use the Onan. It needs the exercise.
