The Level-Up system seems to be what everyone likes. I use wood right now and am considering the Level-Up system in the future.
As for a built in generator, order it! I think that many remember Hurricane Sandy (which the news media called Superstorm Sandy) where a lot of people were without power for days. Nice to have a place that you can go to with lights, A/C, and power to charge the phone, etc. Also, it is nice to stop about an hour from your destinations, light up the genny and have the trailer cool when you arrive. Additionally with a few small parts you can make a hose to connect to the regulator and use up to 100 lbs cylinders of LP in an emergency. During the summer months we carry a small five gallon LP cylinder that we hook up once we are in camp so that we don't have to fight the bigger cylinders out of the trailer as often.