You should be aware that a lot of park and ride locations prohibit overnight parking. That doesn't necessarily mean cars get ticketed very often, but the lots were originally planned for commuters in order to encourage car pooling. I don't think there's a park and ride near Somerset, but FYI for the future.

You can probably lave cars at the Walmart a couple of miles north of the turnpike. They're okay with the RV crowd, but you might want to call and ask. Just take the first left when you get off of the turnpike, on route 601. There's Turkey Hill right at the corner if you want to gas up.

I'm not sure what the on street parking rules are. Fair chance you can find free parking that's legal, but I don't know that I'd say it's safe to leave multiple cars in a residential area for 3 days.