5'er Length Where You Have Issues Finding Campgrounds/Sites

Try this report,and see if it helps. This may not be gospel, but it will give you some idea I suggest you get it straight from the horse's mouth. I would call the ones you plan to visit to be sure. I think it is good idea to get reservations if you are concerned about getting a large enough spot
https://camperreport.com/best-rv-length-for-national-parks/