We were at Hocking Hills last week.
You have a steep climb into the campground but doable.
The sites are short like in most Ohio State Parks. There will be many sites you can use but you may need to park the truck in the grass or on another empty site. Some state parks are very strict about not parking on the grass but I saw many vehicles on the grass at Hocking Hills.
Sorry I can't recommend a particular site. The one we used was very short but double width. It would have been too short for your RV.
It is a nice park, we enjoyed 5 nights camping. I got in 24 hiking miles while there.
Don't forget to use your Golden Buckeye card if you have one. It will get you a 10% discount on weekends and 50% discount during the week.