Suggest you consider an "alternate backstay" antenna. Robust, easy to rig, works as well or better than a traditional backstay antenna, and you don't have the expense and hassle and potential problems of breaking up your standing backstay with insulators.
Search the SSCA board (http://188.8.131.52/DiscBoard/
) for the terms, "alternate backstay antenna" and posts by me (btrayfors)....lots of info there.
I've used one for 18 years now, with no problems and great performance.