We stayed @ Detroit Greenfield RV Park last fall,,, it was the closest for us coming from SW Michigan,,, it is between Ann Arbor & The Henry Ford,,, about 25 minutes from THF !!! There are a few grasses camp spots,,, away from the trees,,, dirt - Leaves - and the lake !!! We only need a place to crash,,, because we were going back to THF again the next day,,, so it was fine for us !!!
There is also Camp Dearborn,,, which is not in Dearborn,,, it is about 35 to 45 minutes North !!! Both offer Camping/THF discount tickets !!!