My wife will dislike this answer, but hardy kiwi might be a good option for your trellis if you are willing to put in the effort to train it and maintain it. The disclaimer there, being, that hardy kiwi is considered an invasive in Pennsylvania now due to an uncontrolled wild population on the eastern side of the state. There are a few threads on blackberries you should read through. Ponca - A new U of A blackberry achieves "pinnacle of flavor"
Additionally, if you are looking for a bulletproof berry, look at jostaberries. My thread here has a lot of good info on different lower growing plants that might fit the bill. BRING ME A SHRUBBERY! (zone 6A)
Also, since you are in western Pennsylvania, say hi in the local chat! Pittsburgh Metro Area