Skip Thayer Lake and go to Three Mile SP
This is a really small campground with a few electric boxes to park your camper on the outside of the parking lot next to the lake and one average tent site with a fire ring and picnic table.
The lake is a good local spot for fishing but I would go to Three Mile State Park to camp with my family, it's just an extra 10 or 15 minute drive away.
Month of VisitJuly