If you Google RV parking at Henry Ford Museum you'll find leads to both campgrounds and parking. There aren't many campgrounds close by. We usually stay in Ypsilanti at the Detroit Greenfield RV Park which is west toward Ann Arbor and probably a 30-minute drive away. I saw one reference that said the museum parking lot is huge and should accommodate your trailer but that overnight parking is not allowed. The best way to confirm that is to call The Henry Ford and ask. I have the impression that surrounding communities do not allow overnight street parking. And I'm not at all sure that overnighting at WalMart would be a good idea.
If you've not been there before, you can get a package rate that includes the Henry Ford Museum, Greenfield Village and the Ford Rouge Factory tour. Each one is worth a day. Expect to walk a lot too, especially at Greenfield Village. When I was in college I was a tour guide in the Village and I remembered the museum itself as being a dusty, dull and boring place. No longer! It's now a bright, cheerful, and fascinating place that easily can take days to explore. Don't miss the early camping vehicles!
If you get into downtown Detroit, the river front has been upgraded significantly. We spent a delightful day there last summer and took a really good river boat tour that went over to the Windsor (Canada) side, under the Ambassador Bridge, and around Belle Isle. The narration was excellent. The tour boat is near the Renaissance Center. You also can take a monorail ride around the downtown area.
Another interesting place is the Tuskegee Airmen Museum which is at old Fort Wayne. The fort is in bad shape but one of the buildings houses the museum which is dedicated to the first black pilots who flew missions during World War II. The museum has quite a few artifacts but the most interesting thing is the video of interviews with the airmen. Their stories tell about life in a segregated Army Air Force during the war and what it was like returning home. There are only a few of these brave airmen left so the narrative about the era in which they lived is fascinating. [Note: As an Army Brat in the same era, I can attest to the truthfulness of their stories.]
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