I was also considering a 42' long toyhauler RV. However when it was pointed out that most Federal Campgrounds have a 30 - 34' length limit, and it is rare to find some in the 40' range, I have second thoughts.
Right now I have a 30' motorhome that I can get into pretty much any campground that I like. Once I even fit into a 26' campsite, by letting the rear end hang over the stop bumpers a few feet.
But starting with a 40' fifth wheel? That does sound crazy. I would suggest starting out a little smaller. Or better yet rent a RV from a friend, or a rental agency, and see how much you like it.
Fred.