We were just in Pittsburgh in June/July with our 28-foot Class A. Absolutely no place to stay in an RV within 25 miles of downtown and Heinz Stadium. We were staying at a hotel across the river from the stadiums (Hilton.....would never stay there again for love nor money) and they had our convention attendees parking in a lot behind Heinz stadium. I'm sure there are parking lots where you could park during the game but suspect they'll charge you double or more (lots ranged from $5 to $20 per day) and not allow you to stay overnight. And driving around the area in an RV....oh brother.
I have not been to the new stadium. When it was three rivers stadium We would park at the place were they made Clark candy bars. It is now a very large bar and is named Clark bar. This is were buses and HM would park It is located across the parking lot of the stadium. Since the new and old stadiums are so close to the same site. I would think that parking would be the same. Just to give you an idea of the size of the parking lot is. They would park 50 buses. 25 HM. and 100 cars this are not actual numbers just an idea. I would call the Clark bar to find out about it. You use to be able to park right at the stadium. If your HM was to big and had to park side ways they would charge you for the spaces you took up. I would also call the stadium.
Good luck and go steelers