We live near there. The places at the Indiana Dunes are hard to get, especially on a busy summer weekend. In fact, we've never had any success getting a reserved spot. We have never tried to just show up and hope for the best. You have some other options. If you want Lake MI camping, there is Warren Dunes about 30 miles further away. There are other MI campgrounds a little further North. There is a nice campground south of Michigan City and you could drive a few miles to spend days at the park.
Dan & Christine (and Molly)
2015 GMC Sierra 4WD Crew Cab Short Bed with Max Trailer Pkg
2015 Jayco White Hawk 27 DSRL