As others have said if you stick to private parks you should be fine. In the west many of the state and federal parks were not designed for larger RV's and while they may have a few sites that accommodate large units the competition for the large sites can be intense because the guy pulling the tear drop will also be trying to get it.
To provide a specific example here is the camping sites available at the Olympic National Park in Washington. Note that larger units can not even get to some of these campgrounds let alone find a big enough site:
Status of Olympic National Park Camp sitesFinally, note that there are no private campsites in the vicinity of some of these campgrounds (for example Kalaloch which is pretty spectacular). For that and other reasons we have a Truck Camper and can go to pretty much all of those campgrounds and use any site. However, we aren't trying to live full time in it either.
That doesn't mean you shouldn't get a larger RV, just that there are compromises as with everything.