Not sure about national forests - but we had a 'day-use boat fee' PLUS camp fees on EACH DAY in one of the South Dakota state parks. We had no boat, came in only to stay the night, and leave the next day traveling.
Needless to say, we traveled fairly quickly out of South Dakota -- we also noticed the COE camp about a half mile away was full. The SD state park had about sixty sites, only seven campers. We had no trouble figuring out why.
State parks that add day-use fees to camping sites are shooting themselves in both feet.