The size (output) of the generator will actually depend on how much wattage you plan on using at one time. At a minimum, I would think to run your basic RV needs (no A/C) you need at least a 2k unit. My choice would be a Honda or Yamaha inverter unit. They are easy to start, quiet, and will do a excellent job up to the 2K draw. There is a Chinese unit (Champion?) that's also a 2K inverter unit that sells for several hundred $$ less than the Honda or Yamaha. I don't, however, have any personal experience with this unit so I can't comment on it. Due to the reduced price, you may want to investigate it.
Add up all the wattage of the appliances you will using at one time and this will give you a pretty good idea of what size generator to buy.
Just a note---if you need more than the 2k output, you can buy a wiring kit to allow you to pair up 2 of the 2k units and double you available wattage to 4k.
Good luck. I suggest you shop on line to find the best price on the unit you want to buy!
Days camping (2015)----88 days
Days camping (2016) ---110 days
2016 Wildcat MAXX 28RKX (33' TT), 2007 13' Scamp
2015 Ram Laramie Hemi
30 years RV'ing
12 different RV's