Exit 76.9 (Sandusky exit) on the OH Turnpike westbound has RV overnight parking with water & a dump station.
Ooh, just looked, if you don't want to go that far, exit 139.5 (Lorain exit, 2 counties east) on the OH Turnpike westbound has the same.
OH Turnpike service plaza listings In case you want to know fuel/eat stops.
Lori-