Coming from Backus, Minnesota, Google takes one through Minneapolis, MN and then Eau Claire, Wausau, and Shawno WI to Ephraim - 514 miles.
Our favorite place in Door County, in the days when we tent camped, was Peninsula State Park.
At the time I had a sail boat and it was easy to drive from the campsite to the launch area with the mast up, no overhead wires. Plus there are many hiking trails, view towers and the relatively protected waters of Green Bay. This was forty years ago, but I doubt it has changed all that much. I see they do have some sites with electricity. I don't know the necessity of having a reservation...
The view of Eagle Bluff from Ephraim is nice:
and there are bays and islands to explore.
While you are there, be sure to try a Door County Fish Boil. It is an experience not to be missed.
Camping near the Dells, Rocky Arbor State Park is nice. A word of warning: Wisconsin Dells is the typical 'tourist trap'. The only thing that I feel is worth doing there are the boat rides, Upper and Lower Dells. If you only do one, do the Upper Dells. If you do both, do the Lower Dells first. Reason, the Lower Dells is nice but not as spectacular as the Upper.
South of the Dells is Baraboo and the Circus World Museum, The House on The Rock, Tower Hill State Park, where they used to make lead shot, this is lead mining country. There is also a natural bridge in this area. A little south of the Wisconsin River, is Cave of the Mounds.
You can follow the Wisconsin River to:
Prairie Du Chein where there are historical things like Fort Crawford, Villa Louis, and the smallest National Cemetery.
Along this route, there are many things to see and do. The internet is your best friend to find them.
Enjoy, and congratulations on your new egg.