KHIO FBO
There's only one functional entity at KHIO that acts as an FBO - Hillsboro Aero Academy.
They have all the services you may need, but are a bit spendy as they focus primarily on their foreign students ($$$$).
If you just want to park, get fuel, and visit the area, there are several RV builders/flyers on the field and they may chime in here to offer a hand. I used to be based there, but am now at S12, so am not able to be of much assistance.