You do not state the size of your MH. Philly is not very RV friendly. Also, because of it being a holiday weekend there will be many organized activities and center city will be very crowded and congested with people and traffic. I do not know of any parking lots where you can park that would be close to the tourists' attractions. There are a few campgrounds in NJ and in PA outside of the city. Hopefully, someone more familiar with the city can provide you some better information. Philly is a mecca for history lovers; I hope you enjoy your visit to Philly.
Ray