Lots of good discussion here.
I do want to steer this thread back to a couple key points if I may.
We are talking about overnight stops at places with electricity in the northern tier, during the two migratory seasons. Which to my observation, the move south ends by the beginning of January. And the move north starts around late March. (snow happens in our home town as early as Halloween, but gets falling in earnest by New Year, and 20 to near 30 feet by April is not unheard of; temps in the northern plains can drop to -40F (or C). Nobody with brains tries to go south by that point)
I am not knocking the following, but they belong in a different thread: We are (or at least I am) not talking about setting up camp in winter conditions. We want to get past the cold part of the country as quickly as possible. Daylight hours are really short, especially for the south migration. We just want to be off the road (with AC power and without a generator rumbling near our bed) when it is dark. Solar power doesn't get you much under those conditions; your tow vehicle-motorhome will be charging the house batteries as you drive pretty much all the daylight hours.
There ARE campgrounds that are open - usually with limitations - during the migratory season. Just not enough of them.
Thank you afidel for mentioning Wisconsin's Black River State Forest. There are 3 campgrounds, two of which are strictly for primitive camping. Castle Mound is touted as 'modern', but the only at-site hookup is electric (and I strongly suspect 15A), and even there, only at half the sites. It is still a long first day haul to get there from home and a bit off our usual route, but I've kept it on the back burner as a possible stop ... unfortunately there isn't much information about the campground conditions in early winter. Castle Mound has only so-so accessibility reviews from RV owners for the summer, and no indication as to how many of the sites with electric are available in the winter. Still, it is worth a phone call.
