Here's what I found out through google search...I guess they used to have RV parking in the main parking lot, but not anymore.
1501 Reedsdale Street
Parking controlled by Alco Parking 412.323.4455. RVs are to park on the other side of the stadium next to the Carnegie Science Center. The Science Center is directly across the street from the field.
I guess call them if you have any other questions about it. Have a safe trip and enjoy the game!