Wolverine Ann Arbor to Chicago - How crowded is it??

Planning to go from Ann Arbor to Chicago in May. Bought the Business Class thinking it had assigned seats as there are 4 of us travelling together. Cost double the fare, but thought it would be worth it to guarantee us all together. BUT apparently even Business Class is first come / first serve on that route. How crowded are those trains in May usually? Considering changing to coach, but if it's a fairly crowded train I will stick with business. Thoughts?