Just as a for-what-it's-worth rant ... we rented our a Class C motorhome to see if we'd like it before we bought and we were faced with that ridiculus fee adder for generator usage. That's a ripoff and just an excuse to up their bottom line. 50 cents per hour would be more like it!
We use our built-in generator all the time and also carry along a 2nd portable one. Considering what you have to pay for them to us a "self contained" RV is supposed to be a mini mobile version of our home, so full power capability is a must and the generator is there to be used - along with the inside and outside showers, microwave, oven, air conditioner, and furnace. Our tenting and backpacking days were spectacular in their time, but now they are pretty much over.