Have stayed at Valley Vineyard Big4 numerous times, get one of the drive through (if you can)
However there's another park (for get the name)and it's not listed in a lot of the guides but it's also owned by Valley Vineyard on the main road just out of town heading toward the airport just near the Shell servo.
Don't know of any freebies in the area, though you can camp at Wollembi Pub for a small fee
Oh and check out Kevin Sobells wines if you haven't already.