Saw this on ebay and wonder if it might work across the transom of any of your boats. Looks like very well made seat.
http://cgi.ebay.com/ebaymotors/HEAV...m14QQhashZitem300232919983QQitemZ300232919983
http://cgi.ebay.com/ebaymotors/HEAV...m14QQhashZitem300232919983QQitemZ300232919983