I have used electric brakes on several trailers. They work. Main problem was
the axle grease seals leaking grease onto the drum surface where the
magnetic pucks slide and the grease greatly reduces (read kills) the braking
action. SS sleeves on the axle grease seal land will stop that. There are
some anti-corrosion parts available but not much. However, there a few
moving parts and as long as the magnets can grip you will get decent braking
action. So answer is, I don't know if they will work OK for you but
contrary to what some might think (say), they will work.

--
Ron White
My boatbuilding website is:
www.concentric.net/~knotreel