Yes - I agree with both recommendations (Niagara Falls and Port Huron). We've stayed at both too. When we traveled with the kids, we frequently made a stop in Port Huron - and stayed at the KOA - Beautiful campground.
Port Huron Township RV Park at mile marker #274 on I-94/I-69 at the Water Street exit behind Cracker Barrel, 1/2 mile from the Blue Water Bridge.
This park is right next to freeway exit, easy off & easy on.
I live 1 mile from this park & stayed here a few times.
This is not a fancy park, but close to everything.
Disregard the website I posted, www.porthurontownship.org takes you to township website but I could not find park information.
Look instead under RV Park Port Huron Township.
This will take you to the park page then you can click the website link.