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 dry camp twice a year... For us the twin EU 2000's work perfectly.....no need to lug that extra weight around.. And space eater... That's just us...I do know folks that like to stop in rest stops..truck stops..walmarts..while traveling..in that case , an onboard generator would be best