This is the lock that I bought recently for marine use. I've only had it in use for a month or so, but it is located just inches above the waterline exposed to the elements 24/7. So far, so good. It has positive reviews.

http://www.amazon.com/gp/product/B000XBJGBU/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1