Replying to myself...
Here is a link to the Arrowhead Park. http://www.kcchiefs.com/arrowhead/apark/
This opens at Noon the day before the game. The entrance is closed at midnight until 6AM and then re-opens for game day. I'm beginning to think this is the best option. But - it would be good to hear from people who have taken RV's there in previous years.
If you tow a vehicle in - that vehicle has in/out privledges but the RV/busses, etc.. must stay. Spots are reserved, so if we did this lot we'd want to either buy ahead of time and coordinate or agree to meet on game day and enter together.