Did a Google map search of that site #57 and it appears to be able to handle any slide size. Here is a link (Google Maps)
and type in " Indiana Dunes National Lakeshore, Porter, IN" And then zone in to the campground. Most of the sites in that CG. appear to handle slides. There are a few that a awning might be blocked by a tree, but in general 90% are nice looking with 2-4 trees near each site for a little shade, but not too close.