We love Big Bay State Park. Great hiking, easy camping with kids, and the sites themselves are very private and quiet. Easy to back in our 31-foot Class C and still had a lot of room in our site to stretch out, cook and for the kids to play. 

Also worth noting that if you're worried about the ferry, they can accommodate just about any vehicle that can go down the road. We had no problem with our Class C getting on and off the ferry, and in fact we had a dump truck behind us on both legs, so there's plenty of capacity for big vehicles. It was around $200 for a round-trip with the RV, two adults, two kids under 6 and a dog.

Stayed here a few years ago for one night. Sites were level, access to the Big Texan Steakhouse was great, and hookups worked great. Road noise and wind noise were a little more than we would have liked, but otherwise it was a perfect place to get off the highway and rest.