If you want a campground east of Duluth for a multi-night stay, we highly recommend a very nice city park campground in Gladstone, MI. It is called Gladstone Bay Campground and is located on the edge of town near the shore of Lake Michigan in a quiet, residential part of town. It has long, level, pull-thru FHU sites for $25/night and the sites are fairly wide and have grass and a few trees between sites. You can check out what others say about the campground
HERE.If you wanted to drive a little way off US 2 for a multi-night stay, you might enjoy spending time on Lake Superior at Pictured Rocks National Seashore, located east of Marquette on the northern coast of the Michigan UP. However, Hurricane River CG is a very popular place with RVers and FC-FS, so you might want to get there early in the day. It does not have any hook-ups, just water, but the sites are large, private, and close to the beach. So, you can fall asleep to the sound of waves lapping up on the shore.
Have a great trip where ever you stay!