It's IP67 rated when used with the "Scanstrut Cable Seal Pack". I just ordered both for my additional rail-mounted panels, to tie into the existing connections for my deck-mounted panels.
I'm also going to use the "SeaStow Rail Clamps" for the top rail, and some additional clamps I have for the middle rails to create a diagonal support for each panel.
You can search the Defender site. Phil also has some water-resistant junction boxes if you check this site's chandlery http://shop.sailboatowners.com/prod.php?7575