list of rv length limits - state parks, Californialength limits for various national parksI did a search of reserveamerica looking for RV sites for a 40' rv - there were 48 parks to chose from near DC. I did the same search for RV sites for a 30' rv - there were 65 to chose from.
Patapsco Valley has 1 40' site and 13 30' sites available (it was closest with 40' sites)
I did a search on reserveamerica for campgrounds in Utah for a 40' rv - 114 parks; 30' rv - 154 parks.
Anyway, the point is, there will be some parks one cannot get into when one goes larger. Whether or not that has an effect on you greatly depends on the type of camping you do. If it is mostly private parks, you like many others here, will have no problems. If you like forest service type camping, your possibilities narrow, especially in some areas.
Best of luck in choosing the right rv for you.