Helpfull people at Stratford Boats and Outboards - they usually have a selection of good quality s/h boat trailers at very reasonable prices.
Call Justin - mention CMBA, - I just purchased a mint fresh water only SBS 750Kg bunk trailer (c/w trailer board) - looks like new, - for half current NEW price.........
https://www.ribsandinflatables.com/used-trailers