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.
As a point- we just returned from a trip and because of ice conditions(and the fact just winterized) had to stay in a motel- newer trailer have a great need for power and batteries will not stand up to long hours of drain. For that generator is the answer.