First off you do not mention price? Second that generator is extremely heavy so even though it may be on wheels where are you going to store it and how are you going to get it there?
Third, Onan does not seem to me to have a very good reputation any more. There are lots of posts about issues with them.
Fourth, do you really need that much power? What sort of RV are you planning to power?
For most casual RVers a small portable generator like the Honda 2000 or the Yamaha 2400 or 2800 are by far a better investment.
To actually determine how much power you need, start by taking a survey of your power needs/wants and go from there. You also need to take into account how often you will actually need to use the generator.
Come back with some more information please.
Don and Lorri
2007 Dodge 3500 dually