I have an article from the May 2002 Saltwater Sportsman. It is an article about a guy in New Jersey who keeps herring and pogies in a pen all season long. He said he got his materials from Memphis Net & Twine Company,
www.memphisnet.net , and 888-674-7638. He used soft netting, 1/2"square, no.9 soft-nylon twine. He made the frame out of pvc pipe I believe
I will try to scan the article and out it up for you.