RV park near Camden, NJ (near Philadelphia)

You're right, the SS New Jersey is docked right across the river from Philly. I've been there a couple of times, and really enjoyed it. There are also other things to do in the immediate river front area, and I believe you can get some kind of combo tickets to see things on both sides of the river. That being said, Camden itself is a very dangerous dump. It is not surprising you can't find too much camping in the Camden area. Depending on how far you want to camp from the SS New Jersey, you can go to Wharton State Forest or others. When you visit the SS New Jersey, please be careful traveling through the outlying areas. Once you get to the park around the river front, it is safe.