Every state park I've visited in the UP (most of them) has had 30 amp hookups, hot showers and a central fill/dump station.
Most even have paved 50 amp pull-through for the monster rigs.
The parks further West are less busy, more than a few hours away from I-75 seems to discourage people. Regarding the weather staying near Lake Superior ... watch the wind. Temps can swing 30 degrees several times a day, and the bugs vary a lot. Wind from the South will bring warm air and BUGS from inland, from the North will bring cold air off the lake and shoo away the bugs.
Favorites: Indian Lake in Manistique (near Lake Michigan), Lake Gogebic outside White City, Muskallonge in Deer Park (on Lake Superior), Fort Wilkins in Copper Harbor (on Lake Superior)
Honorable Mention: Tahquamenon Falls near Paradise, Straits SP in St. Ignace (on Lake Michigan), Wells SP outside Cedar River (practically Wisconsin, on Lake Michigan)
Ask me anything, I make several trips each year to the UP, it's my favorite place in the state.