https://www.winnebago.com/owners/grand-national-rally
It's a week-long celebration of all things Winnebago. Usually most of the main component manufacturers (Freightliner, Cummins, Michelen, etc.) have reps on site and put on various seminars.
There's live entertainment every night.
Camping is on the rally grounds, which are right across the highway from the factory in Forest City, IA.. Electric available at each spot, water at the end of each row (if you're in the middle, you'll need your neighbor's help to fill tanks), no sewer (dump at the city park before arriving). There is a large bath house available.