As a local, I can only provide information. We would not bother camping in walking distance.
Camp Dearborn is a pretty decent place. but a lot of it is FHU parking lot. It is about 40 miles from HFGV.
Detroit Greenfield (no longer a KOA has more shade, most are FHU and is 25 miles from HFGV.
Wayne County Fairground is 6~7 miles closer, but not much (if any) FHU. WE is common and there is a dump.
Sterling SP is a parking lot (zero shade), clean safe and nice, but very few FHU. Electric is common and even water can be rare. It is 35 miles from HFGV.
Harbortown in Monroe is listed as an RV resort (We don't do those). It is 36 miles from HFGV.
RV parking at HFVG is problematic at best if you are over 26'.
I hope this is a help.
You don't want to miss HFGV if you are within 150 miles (maybe 250 - it is that good). Plan at least two whole days. The museum alone is 18 acres under one roof. It is difficult to see in a day. The village is another couple hundred, but you won't walk is all as it contains parade grounds and backlots.
Matt - Whose DW was a docent there at one time.
Matt & Mary Colie
A sailor, his bride and their black dogs (one dear dog is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.