A nice campground for motorhomes is Prairie Pines Campground in Rantoul which has full hookups and is less than 20 miles from the stadium. You can see more at the link Prairie Pines
. There is a park just outside Champaign, but I wouldn't recommend it.
I'll let others answer your question on the parking situation at the stadium. There are always lots of motorhomes there for tailgating, but I don't know what the requirements/costs are.
Should be a great game with a trip to the inaugural Big Ten Championship on the line. Enjoy the trip and root on the Illini to victory!