Well first, are you planning on staying at traditional campgrounds (national forest, state parks, national parks, etc.) or RV parks (private parks that are closer to towns and cities?
RVPARKS should be fine. They can accomodate most everyone size-wise.
Campgrounds can vary greatly. Out here in California, there are some that can only handle 20ft or less, 25ft or less, 27ft or less, 30ft or less. It can be based on the length of the parking pad or the road leading into the campground. The more remote the campground, the more likely there is a size limitation.