We also have a 5th wheel. We bought ours aftermarket and had it installed in the "generator bay" area at the front of the 5th wheel.
As far as needing one, it depends on what type of RV'ing you are going to do. We like to stop someplace overnight on our way to a destination and use our generator for cooking and to charge our batteries so we are good for during the night. We also like to go out on BLM land at different times and just chill and be off by ourselves.
If you are always in a park and have hookups, you probably don't need a generator. Hugs, Di