I have not been to a game there in 3-4 years. But at that time the only on campus parking I could find was in the parking deck by the
Hospital. Obviously parking in deck is not desirable for tailgating.

Off campus, there are shuttle buses from the Friday Center, the Mall, and General Administration building. I think the Mall and FC offer free parking, but you pay for the bus. The Admin building you pay to park, but have a free bus ride ( I may have this backwards). Neither are very expensive. The Friday Center tends to be the most crowded, but also the most fun as it most closely resembles a real college football environment. The Admin building is closer to the stadium, and not nearly as crowded. I don't remember whether they have port-o-lets there or not. If you have a large group this might be your best bet.

One word of caution, though. Both the Admin and Friday Center are on Rt 54 between I40 and town. Traffic going up the hill into town can get very bad. On at least 2 occasions I have gotten off the bus and walked up the hill to the stadium. So either leave the lot early or be prepared to walk. The Admin building is closer to the Stadium so I tend to park here since it is a shorter walk (~1 mile).