Yep been there multiple time and as long as it isn't a holiday weekend you can usually go in find a spot and fill out registration form at office and they will bring you your camp slip.
Not as soon as you rent a spot. Check in is at 3pm
Like other MI state parks check-in is 3pm and check out is 1pm. Lake Hudson doesn't have a formal check in, it's a phone at the main building and it's generally a pretty laid back place. You likely can show up early and stay a little late and no one would be bothered.
As soon as you rent a spot.
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