It is necessary to have a generator in a 5th wheel, I know some have them some don't. We are looking to go to a 5th from our class a and we really don't use ours a lot now.
We don't have one for our 5th wheel but I have been considering getting one. It would be nice to have while staying the night at Walmart's on our way south in the winter to run space heaters and keep the battery charged. I just found this one at Cabela's. Looks like a decent price for the Champion with a wheel kit and remote start.