I haven't camped that far south, we usually like Bull Prairie Lake campground as it's in the forest, by a lake, small, quiet and a little higher altitude than John Day so cooler in the summer. Facilities like your normal forest service campground, no reservations but never had a problem. It's maybe 45 minutes north of there and we make day trips down. April won't be an issue for heat. Shelton County Wayside may be another one to consider. It's also no hookups and is by a lightly used highway but down in a little valley beside it so not much road noise. There may be mosquitoes out by then, and there are ticks through mid summer, but no more than anywhere else.