There's actually good news for owners of boat trailers-- you can retrofit stainless steel disc brakes onto your own trailer and do most of the work yourself... or that's what a couple of mechanics told me. Haven't done it myself, but I've watched it done, and it seemed relatively easy. You need to be careful that you install a solenoid/switch that allows you to back up, though, as surge-actuated brakes will lock on you.
It's been several years since I did the research, so I don't recall all the particulars, but at the time, there was a kit that made the process fairly easy.
My local marine dealer has the details-- Westside Marine in Port Townsend, WA. 360/385-1488. He's sold and shipped a number of kits to people all over the country.