Did you ever find a bale/hay trailer? There's an auction in Nebraska that has a 20' hay feeder listed. No picture so I can't tell if it's a trailer
http://www.vrbasauction.com/Vrbas%2027th%20Consign%20printed%20sale%20bill%20messenger.pdf
http://www.vrbasauction.com/Vrbas%2027th%20Consign%20printed%20sale%20bill%20messenger.pdf