I wouldn't go with anything smaller than the 1000W Honda. A 500W or 650W generator isn't going to put out enough power for decent charging.
I'd go someplace and try a C with the on-board generator to see if the noise and vibration is really that much of a problem. I'd be more concerned with the space the generator and a five gal can of gas are going to take up. And I've never really liked storing gas in small closed storage spaces. When the sun hits that storage compartment for several hours the gas jug is probably going to start leaking gas fumes.
If you watch your batteries at all, and keep them maintained, then you'll never get close to the point of not being able to start the Onan.
I'm not sure if you'll really save any fuel cost. Where's the cost savings of running a small generator for a more hours than a larger generator for a less hours?
Bill
