Lake Le Aqua Na State Park, IL

I don't think most IL SPs have been closed, just a few minor ones that are less-visited. (So far, anyway - but Illinois politics and failure to manage the budget are a subject for another day.) Good idea to call; they should be able to tell you about sites. I know that when we had a 34-foot TT, a quick drive through Lake Le-Aqua-Na didn't show much choice of sites for us. Not sure, but perhaps the IL SP reservation website may show campsite lengths, etc. I remember that at least some of them had quite a slope to them.

Another possibility not terribly far away might be Mississippi Palisades. Probably a little more in the site size you need there.

Good luck!