mobilefleet is right on target. One thing to consider is the size of the generator. I investigated an external generator a bunch last fall when I was thinking about buying a 25 foot travel trailer. What I learned in particular was this: that keen Honda 2000 watt generator will not run most all RV ACs. They say 2000, but the continuous duty cycle is(as I recall) only about 1600 watts. Not enough juice. You will really need a 3000 watt generator. The standard on most Bs on the Road is a 2800 Onan and they work well but are known to be loud. Honda does make a 3000 watter that should do the job, but the weight goes up a lot..dry weight is about 135 pounds.
Now, the hitch rack mobilefleet mentioned will sure carry a 100 pounds easily. I have the very rack he mentions. The problem that comes to my mind is that it would be a two man job to put that baby up on the rack. Yamaha and Honda and others make invertor generators that are all much quieter than the conventional genset. Some guys that have these things on their trailers build an accoustical shroud to cut down on the noise of loud generators, the cheaper generators are very, very loud.
PSW
2013 Phoenix Cruiser 2350
2014 Jeep Cherokee behind it
and a 2007 Roadtrek 210P for touring