I don't use my on board genny all that much but it’s sure nice to have it. Forget to take dinner out of the freezer or want to microwave something then all it takes is a push of the genny button to have power. Hot day and the trailer is still baking at bed time, well fire up the genny and cool things down before bed. Few cloudy days and the solar didn't keep up with the battery’s well a few hour running the gen set and all is well. I don't have to worry about throwing a genny and gas in the truck, setting it up or theft. It was a no brainer for me as I knew it would be used some and the price of the genny is wrapped up in the trailer cost so I wouldn't be running out and spending another bunch of money on a genny that would do half of what my on board will do.
I keep ethanol free gas in my on board tank in hopes I might not have gas related problems.