I've never been there, so haven't seen the parking. Is it wide-open space? No stupid islands or curbing at the edges (unless there's enough space that it doesn't matter) or anything like that?
Usually, big stadiums want big bucks to rent their lots. Some won't even rent you just the lot, they expect you to rent the facility.
But if the place is REALLY worth pursuing, it wouldn't hurt to ask.
If you can get some rough measurements, maybe even sketch a map, I can give you a better idea of how suitable it would be.