I seem to remember that you can only reserve a spot in the Fair's campground for the entire fair. We did see RV's going in and out, but no idea of what the daily turnover is and if they have a certain number of daily/short term stay sites. We stayed at the KOA and really enjoyed the Fair. We don't use RV parks for much other than a place to stay. You might look into the
COE Campgrounds at Saylorville Lake. We have not stayed there, but generally find the COE campgrounds to be nice and a good deal.